I tried to track down a local supplier for the typical light ply.. not the Chinese ARF stuff. I couldn't find a way to buy it local other than the hobby shops, and sites. I do recall there was a wood supplier out in Oregon or Washington that stocked it.. I believe its also known as Italian Bending Ply...
I think Spruce Aircraft carries some light ply, but I think it would only be a deal if you live close enough to pick it up. Cutting and shipping made the price go quite aways up.