I think this is one of the hardest things to do–and one well worth the time and effort! The difficulty lies in that groups and contact info for them changes so rapidly, and there’s no central listing for all of them.  Ask around; check with your local librarian; search a few of the following sites. And good luck!

Yahoo Groups

Yahoo Groups will allow you to subscribe to a choice of email loops. Pick a couple, ask about support groups, get to know folks a bit–and then try them out in person. I recommend putting in homeschool Colorado (or whatever your state) in order to narrow the search.

Homeschool World

About.com Homeschooling