My two favourite online retailers for boat building materials are Raka and Duckworks. Almost all composite materials required can be found at Raka, and their prices are extremely reasonable. Duckworks sells both composite materials and chandlery. Any sort of obscure boat knicknacks - from rope to anchors to blocks - can be found at Duckworks. And like Raka, Duckworks caters to the budget-conscious builder, and has great prices. Between Raka and Duckworks, you should be able to get everything you need to build a small boat (apart from the plywood.