There's a small sawmill on the side of HWY 421, half way between Wilkesboro and Boone. Very reasonable. They specialize in hemlock and locust mill work. Also, any hardwood mill from Wilkes Co and west will carry some locust lumber from time to time. You'll have to call around. Church and Church lumber is a good place to start, but they may be too big to bother with a small order.