Start with GPWA/AGD, STM has some gambling/media buying people too but not purely casino. For CPA specifically I’d also check affiliate program directories and see who is already ranking/reviewing brands in your GEO, then contact them direct instead of waiting for forum replies.
A lot of decent casino affiliates won’t reply in public because they get spammed to death. Have the boring stuff ready before you message: GEOs, license, CPA amount, payment frequency, negative carryover or not, stats access, and if you can do small hybrid/prepay test. If it’s just “we have CPA offer”, most will ignore it.