What dimensions on the wood and what kind of calls are you looking to make from it? I know where I can get some 1" thick butternut, but that wouldn't help much for box calls unless you are making glued calls. Check with Matt McClain for osage as was mentioned, or try Grand River Hardwoods in Pryor, OK at 918-434-2870. If you call, ask for Virgil and tell him Wendell Rye sent you. Be ready to talk awhile.
Virgil and Wayne are good folks and will treat you right.