Morph,
What kind of plywood are you looking for. While it is possible to buy veneer separately, virtually all plywood has some type of veneer facing. Any good lumberyard (as opposed to the big box stores) will usually stock a variety of plywoods in different thicknesses. My local lumberyard (
The CT Woodgroup) stocks about a dozen different kinds. I don't know if they ship or not but it will give you an idea of the types of plywood that a real lumberyard carries.