Hello Donald,
I have been buying my wood and plywood from
Hogan Hardwoods & Moulding they may have one in your area. Or look through your phone book for a HardWood dealer. I have saved about 3 to 4 doallars a board foot on some of the wood I have bought from them compared to Lowe's or HomeDepot. I also found that some of the plywood you buy at one of the big name salers is different than what you can buy at Hogans or a Hard Wood dealer. The Oak PlyWood I buy from Hogans is a better grade than Lowe's or HD and a little more expensive but for Cabinets or Display cases for me or others I will pay the extra. This is just my opinion.
I also am using the MinWax Stainable Wood Filler and I also use some that I have picked up from Walmart. I will sometimes use the prestain on it before staining and have also found it is sometimes hit and miss on staining plywood.