there are SO many unrepresented yet searched for gay niches.

office guys, business men

twinks in underwear

men in underwear

muscle men (only topbucks has this, and their site is not great)

uncut cocks (only pornkings)

mature men (pythonpays has one, and topbucks, but they sort of miss the point of the niche, imo)

grandpa aged men

these all come to mind first thing.