Hard to advise here. If some straight guy told me "I want to hang out with more gay guys, but I don't want them to hit on me", I'd just tell them to hang out with them, and if they made a move, rebuff them. "I'm not interested in guys sexually." That would presumably stop the present move, but wouldn't preclude anything happening in the future.
But what you're asking goes beyond that a bit. You don't just want to be "off-limits" to them sexually - you want them to accept you as "one of them", as it were. And I just don't have any advice for that. I mean, I hang out with all sorts of people - gay, straight, male, female. And the dynamic does change with whomever I'm hanging out with, based on our interests and personalities. But it's usually along interest lines - I talk sports more with my sports-loving friends, and music more with my music-obsessed friends. I don't have a "gay group" I hang out with, specifically. I can talk about gay stuff with my gay friends, or even my straight friends, and they're cool with it, because we're friends, you know? We can talk about whatever. And I guess I can talk about everything enough that I don't feel a lack. I don't feel like I need - or even especially want - a gay group to talk to. If I do, there's this website, I guess.
I supposed the best move is just go out and make friends. And as those friendships deepen, you can be more of yourself around those people. Rather trite and simply advice, but there it is.
Lex