I don't know of any really bonafide "trap gun retailers" in Houston. Collectors Firearms probably has the best selection of older used models and may have one or two new ones. All of the other dealers occasionally get in a good gun or two. An example is Fountain Firearms. There are others. If you are looking for a good, new BT99, go to Gander Mountain near Hwys 59 and 99. I haven't been there for about six months, but they still had some they opened their doors with. Trapshooting is not big in Houston like it once was, but the ones that shoot regularly, do so with a passion!! I suggest you go shoot at the Metropolitan Gun Club which is now located south of town and off of Hwy. 288 near Angleton. That is the only place in or around Houston that really shoots trap. The regulars can probably point you to a good place or two and may have a safe queen they would let go.
I don't know why. It just isn't anymore. It was long ago. Houston is home to some of the world's best sporting clay shooters though, like Bobby Fowler. Greater Houston Gun Club used to be skeet and trap. Now it is primarily sporting.