I'm no expert on how to do this, but I can tell you what worked here...
- Sail frequently and start talking to the folks at your favorite local sailing spots
- Go to a regatta or two and meet the cat sailors from your area
- Start a discussion on this forum about your localing sailing spot, set up informal meet-ups
- Post a message at any local yacht/sailing clubs that support catamaran sailing
- Check the NAHCA roster for members in your area
- Talk to your Division Chair
- Take your friends and relatives sailing and convince them they need a hobie
Be patient and you'll find some like minded people.