I'm midway through the rebuild of my 1964 Powercat, and I've purchased some supplies from Noah's Marine. They are located in Ontario, their prices are fair, and they have a good selection.
http://www.noahsboatbuilding.com/index.asp
There is also Pride Marine, also located in Ontario. I haven't purchased anything from them yet, but they seem to have a good selection as well.
http://www.pridemarine.com/index.cfm?page=home
I don't know exactly where you live, but you might be able to find a boat repair shop in your town. I called everywhere listed in the phone book, and no one had the stuff I was looking for, and no one could suggest anywhere to me. Then I just happened to drive past a building with "Mr. Fiberglass" on the door, I went in, and wouldn't you know it was a boat repair shop. I ended up buying my resin from him as he gave me a fair price and free advice.
I'm in Regina, SK, btw.