Ok I stand somewhat corrected, repair or modify CB radios, No ...but as far as external hardware is concerned many of them (not all) have a very good selection of antennas, mounts and a various assortment of cable repair items such as replacement cable ends, connectors and adapters as well as various antenna mounting bases and replacement mikes etc..
Quite often the quality of the items they carry is much better than those carried by places like radio shack who often only give lip service to CB items. I have been messing with CB,s since the very early 70's and short of CB and Ham radio specialty shops (which these days are becoming hard to find) I have found truck stops to be the best and most convenient source unless you go online.