We found families in a variety of ways. Our province (Canadian) has a provincial advocacy group, and I signed on to be the local coordinator, so any requests for advice and meet-ups from people in our area are directed to me.
I've also had good luck with posting notices in libraries--we've gotten in touch with a number of homeschooling and distributed learning families that way.
And some of it is just serendipity: I was on the parents' council at my daughter's small school and met several parents with similar concerns (although it took ages to find that out! talking about fundraising doesn't naturally lead into discussions of gifted kids).
