It's not really anywhere specific although there are a quite a few of us floating around. The chuunin (http://www.livejournal.com/community/chuunin/) comm has a number of them, but we only come out of the woodwork when someone creates a topic about crack pairings.

There's also a comm devoted to crack pairings, but it seems as though it's more geared towards fanfiction than actual discussion.

You could also try another community called narutalk (http://www.livejournal.com/userinfo.bml?user=narutalk/) which is devoted to indepth discussion about Naruto. It's kind of slow though and not necessarily concerned with pairings, but you could start a pairing related topic if you wanted.

If somebody wanted to start a community devoted to the discussion of unusual pairings or ideas in general, I'd be more than happy to join.