Jeff,
I'm probably missing someone, but the only places I've found it was the Hardwood store. And I'm not totally happy with that, as its skip planed to you never know what the actual thickness is gonna be. What I really want is rough lumber from a sawmill but I've come to the conclusion nobody will saw 12/4 unless you order it.
My brother and I make a road trip of it and spend some good time together.