Does anybody know of any International Folkdancing (Balkan, Greek, Israeli, etc.) happening on a regular basis in Zurich?

Hi. You may want to have a look at this thread and/or get in touch with John (jbendix). Baden is a 15 minute train ride from Zurich.

There used to be a group that met regularly in the Rötelstrasse Gemeinschaftszentrum. I haven't been there for many years though so can't say whether they are still going.