If you're willing to look in the SF Bay Area there's Beronio Lumber in SF and Truitt and White in Berkeley. I've bought air dried WRC stock from Beronio and I know a couple-o-guys who recently bought stock from Truitt and White. Quality ... don't have too high expectations. You might find good stuff, you might not ... mine was passable but not the best. Flat grained planks were very tough to find. Lot's of folk say to try Redwood. I looked and couldn't find anything that didn't have a knot every 18 inches. When I mentioned the words "clear" and "wood" to the lumber yard folk they just shake their head no!

Good luck!

Ken