One way I know to get the word out is ask the club secretary(or someone who has a roster) for names of people that have catamarans. That won't get the ones that have boats in the back yards, but at least maybe get the ones who day sail to come out. Make sure that the seminar is based on boat handling and not racing. Sure, they'll be racing involved, but not intense. Or putting a flyer on the bulletin board of the local sail shop. I know there are sailer's in my area that don't go to the local lake very regularly, don't keep the boat at the dry dock, but they do go to other places to sail. However, they do drop in the local sail dealer on a regular basis. So, a flyer there might not be a bad idea.

Those are a couple of ways that I know of to get the word out.