Hey, Capri - Look at this Website I found: http://www.roundsing.org/ - lots of good stuff there. Also, you might want to take a look at what I got out of a Goodle Search for singing rounds - Click here.
Another good resource for rounds is the Rise Up Singing Songbook from Sing Out! (click). It has lyrics for some 1,200 songs - but it also has music for probably a hundred rounds.
-Joe Offer-