Sorry, I saw your post in the "recent answers" page, and though I'd help you out. =) If you are looking for a community on a certain topic, just input that subject or some related keyword into the search box at the top of the page, and then choose "interest" from the pull-down menu. If a comm has that interest listed in their interests, then they will come up in your search. Otherwise you might have to try different keywords...

And if that fails, just google "livejournal community" plus whatever you're interested in, and you might find something. =)

Hope that helps! =)