I just moved back from Houston a year ago.
Quality Feed & Garden in Houston is worth checking out. Typically a lot of Brussels material but the owner does purchase local material as well. Ask for Ken, great guy and board member of Houston Bonsai Society. Perhaps call ahead and ask about TX natives/yamadori.
The two JRN nurseries are Vietnamese and have a lot of tropicals. Worth a quick visit if you're in the area. No natives really except nursery stock.
Timeless Trees in Rosenberg is definitely worth the trip. Go see Hurley, open Fridays and Saturdays. He has a great selection of material and really nice stuff. Great dude too and also a board member of Houston Bonsai Society. Likely had TX yamadori kicking around.
Last but not least. I know of a guy 1.5~2hrs drive out of Houston who digs native Ashe Juniper and Cedar Elms. His material is incredible and he takes great care after collection. You can message me if you're interested in this option and I'll see if he'd be available for a visitor.