There is a group in Michigan called CRAM (of which I'm a member). We organize and/or participate in about 7-8 regattas a year, including a couple in Northern Michigan (Charlevoix in early June and Higgins toward the end of Sept.) You can find our schedule here: http://cramsailing.com/regattas/schedule/
The Portsmouth fleet seems to be growing this year with an H20, several H18s and H16s joining several of the regattas. We'll be in Tawas this weekend. Looking forward to some fantastic weather and conditions.