You can try Toys for Big Boys on Nacogdoches Rd. or Full Throttle Hobbies on I10 in Boerne. It really depends on where you are staying at but I like the people at Full Throttle.
I think they are both open for practice runs with a donation. Toys for Big Boys is closer to you but Full Throttle Hobbies has a more technical track. Give Full Throttle a call at (830)537-5061, they are very open to new people and their track is very new. The trip up I-10W is not that bad.