I don't climb but I've been in a few climbing/bouldering gyms and I gotta say it's one of the friendliest communities I've ever been around. I would think about the coming a regular at gym and slowly meeting people there. You can ask anyone for help or a question about a route and it's an easy way to get to know people. Just don't rush it and expect to make friends overnight. And if you don't actively play sports but still enjoy playing, intramural leagues in your city are another great option. I play coed leagues because they're the least competitive and you get to meet new people. You can sign up as a "free agent" and they'll put you on a team. You can even join with your sister or nephew of you guys share any sports or other interests in common. Even a bowling league sounds fun.