All the fight/evade reduction cards that enable Exploit Weakness (not including Darrell Simmons):

Guardian

• Bolas (The Scarlet Keys #25)

Seeker

• Anatomical Diagrams (Echoes of the Past #108)
• Map the Area (The Scarlet Keys #48)
• Expose Weakness [lvl 1] and Expose Weakness [lvl 3] (Undimensioned and Unseen #228) and (Heart of the Elders #195)

Rogue

• Momentum (The Search for Kadath #115)
• Stealth (and Stealth (3))

Mystic

• Wither and Wither [lvl 4] (The Wages of Sin #157) and (Before the Black Throne #321)

Survivor

• Makeshift Trap (The Scarlet Keys #100)
• Grizzled (The Scarlet Keys #101) (after taking the nemesis upgrade).
• Improvised Weapon (The Forgotten Age #33)
• Impromptu Barrier (Shattered Aeons #312)
• Gumption [lvl 1] (The Scarlet Keys #112)
• Quick Learner (Stella Clark #30) {Thank you Kryha30}

Neutral

• Flashlight [lvl 3] (The Scarlet Keys #122)

-- Other:

• Ruth Westmacott??! (Dark Revelations #20)

Couple things to note:

First, between reducing fight to 0 or evade to 0, there are more tools (in Bolas and Flashlight (3)) for reducing evade than for reducing combat. There is also less opportunity cost in choosing to take Exploit Weakness in an evader's deck over a fighter's deck; fighters will likely already have plenty of tools to remove enemies from the board, and so have less need for Exploit Weakness.

Second, did you forget about Anatomical Diagrams? I sure did, but now you should never forget because it gives the most fight/evade reduction of all the current options. Even Flashlight (3) only compares on the evade side, and that's a level 3 card! What a dark horse candidate.

Third, before you're tempted to put every fight/evade card listed here into one deck, make sure you can actually make good use of them. The Survivor and Neutral cards don't necessitate anything, but Bolas requires you pass a decently hard check, and Anatomical Diagrams demands a high sanity investigator or horror-resilient investigator, or both (Map the Area on the other map is usable by almost every single investigator).

Forth, this list shrinks to only 3 entries if you want to trigger Exploit Weakness on Elite enemies, which is entirely reasonable; effectively test-less 3 damage plus an evade is nothing to scoff at. If that's your goal, only Map the Area, Gumption, and Flashlight (3) will cut it, and at that point you should consider Darrell the only viable investigator to make those cards shine, since they stack with his investigator ability.