506. Torque

508. Brutus

532. Plastique/Bette Sans Souci

536. Nate Heywood (robot)

542. Cameron Abrams

545. The Commander

548. Chief of Staff in National City

428 Eddie Slick (Earth-1)

Cleaning out the clues:

481. Original; high school student when last seen; close friend of cast character during teen years J**IE
487. Original; unrevealed; villager in an African nation  F*YIN**LA
511. Comics; CEO; The Power Company; had nannite-created powers BI*MAX /  JACK *P*EER
522. Original; nation's President; gave a speech on a late hero **AW
541. Original; government agent; electrocuted underwater ALEX *C*TT
546. Original; slave; whipped for accidentally burning cloth prior to being freed by heroes MAR* [LOCKED; characters found at time of locking: ABCDEFGIJKLMNPRTVWXZ2345780]
551. Comics; reformed criminal; The Flash; powers include telephathy, empathy, fear inducement, illusion inducement P*YC* /  BA**IR MALIK
554. Original; government agent; hunted a villain who killed him T**NG
555. Original with some comics elements. This one's a bit complicated. In one sense this is a separate character than one seen earlier (which is how Arrowverse Wiki originally treated them as) but subsequent evidence (from after I created this collage) places them more as the earlier character themself (previously found); adventurer as such; Flash Comics (comics elements); if separate character, they share DNA of a major character mixed with an alien's *ARA LANCE (CL*NE)
557. Original; high school student; ex-boyfriend of cast character *EAN *MIT*
558. Original; likely student of any; son of a later superhero AKI* YAMA**IR*
568. Comics unnamed, radio show named; vigilante; Action Comics, named in The Adventures of Superman; killed by counterpart of main character JAME* *L*EN'* EART*-X D*PPELGÄNGER
569. Original; drug dealer; sold drag that turned people into rage monsters KE*IN **GGIN*
573. Comics (gender swapped/different real name); cultural anthropology professor turned criminal; The Fury of Firestorm; could animate objects BLACK BI**N / MINA C*AYTAN
577. Original; housewife/restaurant assistant; supplied the burgers' secret sauce R**NDA BEEMAN
578. Original; pastor; lived in Odessa, Texas in 1925 P**ELL * [LOCKED; characters found at time of locking: BCEFGIJKLPTVW2780]
579. Original; science centre owner; secretly worked for season main villain D**G MILLER
580. Original; unrevealed, likely student if any; has alien for a pet ALANA (*PIKE'* **NER)
581. Original; gangster; skipped town to avoid main character MARC** *T*CK*EIMER
587. Original; high school music teacher; surname is a music term **ARP
596. Slightly earlier (same episode) character this continuity; unrevealed; killed a cast character's father in a drunk driving accident BRETT C*LLI** (EART*-2)
599. Original; unrevealed; attended daughter's wedding but ended up making out with the would-be groom M*. *INCLAIR'*  M*T*ER
603. Comics; unrevealed; Batman: Shadow of the Bat; born with mental illness and prone to attacking others AMYGDALA /  AAR*N *ELZINGER
604. Comics (gender swapped, so slightly different real name); criminal; The Flash; can induce vertigo T*P / R**A DILL*N
608. Comics (likely different real name, Arrowverse version missing first word in code name); criminal, weapons dealer; The Flash; can create box-like force fields BL*CK / VANE**A JAN*EN
609. Original; scientist; alien with thorns on his forearms R**AN V**E
610. Comics; serial killer; The Fox and the Crow (real name), Green Arrow (code name); obsessed with main character's earliest vigilante persona *TAR CITY  *LAYER a.k.a.  INMATE ##22 /  *TANLEY  D*VER
613. Comics; assassin, CEO; Young Justice; created an enormous destructive tidal wave RIP R*AR /  R***ELL  R*GER*
614. Original; newswoman; interviewed counsellor on anti-vigilantism bill JANE W**D*
616. Comics; vigilante; Batwoman, but inspired by character from Detective Comics; only seen in a photo KATE KANE (EART*-##) [For this one I'm locking the numbers as this one's now too easy to guess otherwise]
623. Original, though name might be a nod to two real life people; business founder, investment magnate, philanthropist, socialite; held a fundraising gala where she spokie with cast characters looking for her son T*ERE*A MERKEL
624. Original; unrevealed, likely student; cast character's first cousin once removed C*RI*
625. Comics; nuclear truck driver; The Flash: Iron Heights; has power to emit dangerous levels of radiation FALL**T / NEIL B*RMAN
626. Original; crime lord (code name refers to another occupation that he doesn't actually have); took over part of town after an earthquake T*E MAY*R /  XAVIER REED
628. Original; cultist; part of a coven wishing for old deities to be worshipped FEI*A [LOCKED; characters found at time of locking: ABCDEFGIJKLMNPTVWXZ245780]
631. Comics (indirectly); posed as chief of police; The Flash Secret Files and Origins; replaced main version of the character DAVID *ING* (MIRR*RVER*E)
636. Comics (comics version's first name unrevealed); technology firm employee; The Flash; fired from organization and then killed for being whistleblower GENE ***KK
637. Original; arms dealer; came to town to sell a shipment of stolen weapons but was interrupted by cast character LE* M*ELLER
639. Comics (indirectly); timeline protector; Hellblazer; mistakenly believed herself to be the real version A*TRA L*G*E (R*B*T)
643. Original; bus driver, criminal; stomach slashed by major villain KEI**A M**RE
646. Original; unrevealed; gained powers in an experiment JA*PER T*WNE*
647. Original; criminal; right-hand man for recurring villain **ECK
648. Comics (prototype from magazine); vigilante; Action Comics  (prototype from Science Fiction: The Advance Guard of Future Civilization); villainous counterpart of a superhero **PERMAN / KAL-EL (EART*- T*D22)
651. Original; councilman; ally of major villain K*LLEN*
655. Original, but resembles character based on comics; mobster; resembles character from Justice League of America; seen in artificial reality C*TTER M*RAN
656. Original; doctor; assigned to care for main character RAFAEL R*DRIG*EZ
657. Original; police officer; provided superhero with intel AN**N
662. Comics; drug dealer; Green Arrow and Black Canary; attempted to murder a police detective *EAN **N**
664. Comics (different real surname); student; Flashpoint; had the power to harness electrical energy BLACK**T / FAR**Q GIBRAN
666. Original; named after real person but not a true counterpart; criminal; kidnapped major character's son J**N BYRNE
667. Real person; astronaut; major villain impersonated him J**N *WIGERT
670. Original; anchorwoman; often reports on main character's activities *ANA *EWITT [LOCKED; both remaining letters the same; characters found at time of locking: ABCDEFGIJKLMNPTVWXZ245780]
671. Comics; criminal, orphanage head; All-American Comics; test subject for major villain CYR** G*LD
674. Original; unrevealed; sibling of major villain *RLIN DWYER'* *I*TER
676. Original; criminal; robbed blood banks for sustenance *ILA* W*ITE
677. Comics; astronomer, assassin; Crisis on Infinite Earths; may have replaced another character with the same code name due to the Arrowverse Crisis DR. LIG*T /  KIMIY* ****I
681. Comics; newspaper intern turned police detective; Showcase; mistook main character for her husband IRI* WE*T-ALLEN (EART*-2)
683. Original; unrevealed; fan of major character's writing D*RI*
687. Folklore; probably none; folklore of the Americas; fugitive from evil realm C**PACABRA
688. Original; unrevealed; accused of being a witch JANE *AWT**RNE
689. Original; music student graduate; attended University of Cincinnati VANITA RIP**N
696. Original; night club owner; main character slept with his fiancée MAX F*LLER [LOCKED; characters found at time of locking: ABCDEFGIJKLMNPTVWXZ2345780]
706. Original; singer; participated in reality TV competition *A*CÉY
708. Original; football player running back; testified against murderous brother AP*LL* TE*L**
710. Original; scientist; wife of someone who was impersonated for a long time TE** M*RGAN
712. Original; unrevealed; was seen as candidate for human trials DERRICK *IMM*N*
713. Original; director; worked for major studio in 1937 ARN*LD C*LE**N
714. Original; police officer; killed in an ambush J*NE*
716. Comics (indirectly); science based employee to the extent applicable; Action Comics; counterpart of recurring character ALEX DANVER*' FAT*ER (*B*IDIAN PLATIN*M)
717. Original; scientist; ally of main character's mother JET*RIAN IND**TRIE* *EMAT*L*GI*T (note: while not named in the show souce sources claim she's DR. T*VA; I'll accept either name)
718. Original; unrevealed; version of another character, attended a World's Fair EDIT* B*ARDMAN
723. Original; federal agent; killed by cultists DEM**
729. Similar to comics character with different code name and real name; doctor turned criminal; Wonder Woman;  augmented herself using stolen technology  CYBER-W*MAN /  LA*RA  WA**INGT*N

 

It's been a day since any guesses . I can add another letter but it will cost 25 bonus shots for the next letter down the pipeline or 40 if you want to pick a specific letter (which could potentially be the next letter anyway).

I spy...
Someone who was probably born on a Monday.
Someone who mistook a guy for her husband and tried to make out with him.
Someone who killed the mother of someone found in the past few days.
Someone who was originally a humour character in the comics.
 

555. Sara Lance (clone)

558. Akio Yamashiro

573. Black Bison/Mina Chaytan

579. Doug Miller

581. Marcus Stockheimer