Tom,

Have you tried Google or your favorite search engine for a location near you. Shipping sheets of plywood might not be cheap.

You don't give a location, but in my area a chain called Windsor Plywood would be the supplier of choice, I think. Not sure you can get pre-sanded edges though.

They have a website. There are a very few American stores and a lot of Canadian ones.

KarinL

Here is a link that might be useful: Windsor Plywood locations