The simple way to find gay forums is to scroll down
the list of forum titles until you find some that are
matched or close to what you're seeking.
You may even have to go through several pages to find
forums that fit your criteria.
The searching seems tedious, but it's better than
not knowing if they exist.

Chances are that the forums you're looking for
may exist, even if they are old topics from years ago.
By searching, it also helps avoiding the creation
of duplicate forums if one already exists.

Other than that, you can also check the Members Groups
listing to see if there are any Gay groups that
may match your interest and/or location.
Hope this helps.