WoodenBoat magazine hosts one in different parts of the country, and there's one called a Messabout sometimes. It seems like most of them are on coastal areas - I think one was around Houston a couple of years back.
I found another site for plans for building your own -
JEM Watercraft - Canoe Plans, Kayak Plans, other Boat Plans
You can even get free plans for a 13 ft kayak - which I DLd and may try to build sometime.
Since I have a couple of paddle boats already, I want to build something to sail. I think I will build a mouseboat called a flying mouse. Theres a Yahoo group for mouseboats with some pictures, and I have a book with plans.