I'm searching the web for large sheets of plywood and found this site. OK. it's located in Australia but they do export to the USA. You would need to send them an email to see who distributes the ply in the US. The range available is enormous. I will be contacting them in the morning for more more specific info on costs and delivery. The info might be helpful to you fellas in the US. I will let you know what the prices are when I get the info back. The range of plywood looks wonderful.
Check it out here. I hope you can find this stuff in the US at a good price.
http://www.dmkforestproducts.com.au/about_us.html
Kody