I am up against the same thing here. I can get hardwoods but not much else. The "Traditional" places as you called them are useless, here at least. But the old school building suppliers are not much better either. I have one I have free run of and and I can hand pick, but there isn't much to hand pick from!

My best bet is redwood and cypress. I can find redwood at some of the building supplies. Cypress is carried by most of the hardwood dealers. The Hardwood guys cater to cabinet makers and a few furniture makers generally. So you and I are out of their area of expertise.

Best bet is call and see if they have any of the wood(s) you want and then go look.

I have settled on buying the best I can find and then resawing it and scarfing it into longer lengths. There just isn't much other choice frankly. I am going to build an improved scarfing jig for the table saw. I will post some photos once I get it done.