Hey ratz. There was a thread about Austin a while back that can be found here: Waxahachie & Austin Texas Cycling Routes It may have some answers for you
I’m originally from Austin but no longer live there, so can’t help much. Austin does has a ton of great bike shops that could help. You could try to get in touch with the people at Austin Yellow Bike (the local bike collective) and they may be able to give advice. Cycleast is a shop run by a friend of mine, but it’s a bit far from Round Rock.
Hope this helps!