Many of the builder/supplier businesses listed in the WCHA directory will sell canvas and will ship -- make a few phone calls and I'm sure you can get what you need. I suspect that a smooth repair at the sponson will not be easy -- and I suspect that whatever caused the existing failure of the canvas will cause other failures in the future -- something to keep in mind as you choose a course of action.
As to paint, Dave Wermuth's comments above are on the mark -- high-end marine enamel (e.g. Interlux, Epiphnes) is available from a variety of sources -- Geoff Burke at Chocuroa Boatworks in our directory handles Epiphanes, for example; Hamilton Marine, Kirby Paints, Jamestown Distributors and others handle marine enamels, there are a number of marine supply stores in Rochester, and most any hardware store or paint shop can sell you good enamel house paint/porch and deck paint/Rustoleum if you prefer not to use a marine enamel -- many here have been quite satisfied with such paints.