There isn't a good place to find the Tribes now that Communities are the center focus. Travelfeed, Naturalmedicine, Buildit, LeoFinance and StemSteem have their own frontends. They have their own tokens too, which you earn on top of Hive for using their frontend or Community.

The best way to find them is to go to the 'About' section of a Community you like. If they have one it should say so there.