This should be of interest for scratch builders:

http://www.aircraftspruce.com/ sells all of the common types of plywood we use in models... in sheets from 2 ft X 2 ft to 4 ft X 8 ft.

Its very nice to be able to skin a large wing in one piece of 1/32 or 1/64 ply. Due to needing less epoxy (the ply doesn't soak up as much when skinning the foam core OR when applying glass cloth) you can end up with a lighter wing that is far stronger than if you used 1/16 balsa, with less work.

2 ft X 4 ft sheets do not impose oversize shipping charges and will serve for all but the largest models. If you build a lot of larger models you might check with your local airport and see if someone there orders large sheets of aircraft plywood... ask them to add your larger sheets to their order.

My order of 1/64, 1/32 and 1/16 plywood just arrived. Very well packaged.