Epp's likely has stock blanks. Any blank won't be exactly cheap so you'll want to teach yourself stock making with some cheaper hard wood. A slab of birch or beech shouldn't cost too much.
There's always somebody around that is having a tree cut down. A 4 foot x 6" log of birch, beech or maple will do nicely. Get the bark off quickly and let the log dry for a year or so.
Like RockChucker says, oak is far too heavy. Some oaks(white, I think) splits as it dries too.Forget E-Bay for anything. They financially support the people who think you should not be allowed to own any firearm.