Not exactly local, but there is a nice rock shop in downtown Llano. Great day trip, especially if you pair it with a visit to one of the biggest rocks in the state, Enchanted Rock.
If you make the trip to Llano, go find some Llanite. It's only known to be found in the Llano area. My old man took me there 20 years ago looking for some
Definitely not local, and I'm sure that the corona thing has closed it down, but years ago, there were several places at Traders Village with pretty neat stuff. Might not be around anymore though.