Where can I find regattas ?

http://www.sunfishclass.org/ (main site for the class - will probably post a 2010 schedule in the spring)
http://www.sunfishclass.org/midwest/blog/ ("official" blog for Midwest, but isn't updated that frequently)
http://www.sunfishclass.org/archives/2009/2009-sunfish-regatta-schedule.pdf (link to 2009 schedule - this will give you an idea of where races were this year - scroll down to the pages 17 to 19 for the Midwest schedule)

You might also join the Sunfish Midwest Yahoo group:

I'd also look around online - you might find a local club that races more frequently. For example, the Wawasee Yacht Club in Syracuse, IN http://sites.google.com/site/wawaseeyachtclub/

good luck,