You can find them all at
http://www.21orover.com/discus/messages/43/61854.html
Many have maps and other data, free of charge

I've used this one:  http://www.kaleus-clubindex.com/kaleu/fkk-en.php.

It's a pretty current listing of both FKKs and Partytreffs.  It's sorted by city, which is good.  Most have a link to a website.  If you don't speak or read German (like me), Google translator works reasonable well.

Face it, it's very hard to have a bad day at an FKK and hard to have a bad day at a Partytreff.

If You Can Speak German...

Roemerforum is just the best resource by a zillion light years. You can play with the Google translator and see how it works for you. My German is pretty rusty, and more and more girls speak English these days now anyway.