3mm or 4mm plywood is pretty easy to find. It takes more work to find even thinner plywood. Especially with the little boats, it is sometimes a better result to do CM with thin plywood, instead of stressforming 3mm or 4 mm thick plywood.  Its not cheap though.  Thanks to Al, building my 20′ tri.

The 2mm ply is from the following link:
http://www.worldpanel.com/products.asp?cat=8&pg=2
The 1.5mm from the this one:
http://www.boulterplywood.com/