There is already a similar
TOPIC being discussed in Meta. Might take a look there and get some forum leads. Not sure any other forum is really half as big as this 1 though and likely everyone with accounts here has probably made accounts on the other forum, so marketing opportunities that would be good for clients are very small. Just my 2 cents.
The topic you mentioned is similar to what LM asked, but not specifically. LM wants to know about casino forums or forums with a gambling section. As we can see, some of us have already submitted links to some forums. But I agree with you that these forums don't have enough traffic for a client to consider advertising their product on them.
Most of these forums don't allow signature campaigns or similar advertising. The advertising is mostly handled by the forum owner and staff themselves. They sell the ad space to companies, and these forums don't have loyal users. They mostly get visitors from search engines. We get loyal users here because of the opportunity to earn from the signature campaign.