Madison has an active scene, but isn't the easiest to find with the active collegiate scene and 3 event scene here. Most of the Dane and Rock county riders hang out at MidwestWakeboarder.com which is a smaller version of this site use for finding thirds.
Other places for finding thirds used to be Redline Watersports just off of 51 by Mcfarland. They used to have a list of people looking for thirds, I don't know if they are still doing that.
Otherwise if you have a facebook hop on and check out the MidwestWakeboard.com Fall Free Ride where people exchange gas for pulls all weekend. This year it's October 1st in Janesville Wi. There are usually about 100 people over the weekend that come and hangout. Or make friends with people on the event page before it even starts.
I'm a student up in Madison and have been pulling the wakeboard team the last few years. We run on Mendota during the week but monona weekdays has our other boat which pulls 3event and wakeboard practices.
Since i'm in school my time has been more limited but I've been riding, coaching, and competing for years so if you wanted some pointers/lessons let me know and I'd be happy to help you out on the water!
Hope all of this helps!
John Zdeblick (JohnnyZ)