I am a member of a group on Facebook that is exactly that. It's called Sofia Conversation Swap. They meet weekly and have over 300 members (Bulgarian and foreign).  I haven't had the chance to go yet (still living in the U.S.), but plan on attending when I move. In case anyone is interested, their URL is:

http://www.facebook.com/editprofile.php?sk=contact&amp;success=1#!/group.php?gid=96844621075

Cheers!