There are generics for a huuuuge variety of weapons in the game. From the code point of view, this is good for the health of the game and they have been well designed, especially after something like a year-long effort on Quartermaster Jinx's part to balance them all. From the IC point of view, some of them are very hard to get and therefore very 'chic' and distinctive on the character who manages to do so.
There are ways to customize them too - at least in the sense of modification. Personalizing them is an old idea which has been asked for and not supported in the past.
The gunsmith role in this game is less about being an inventor and more about being a service provider, one who is very in-demand since the situation in Withmore regarding legality and supply is so touchy.
Hope this helps.
Weapons however, there are a great number of them in game and hoslters/scabards for most of them. Custom weapons would create bloat and increase the size of the game without adding very much in terms of RP.
Guns can be modified and customized to a higher degree than most weapons however, and if you are interested in that, I suggest learning it ICly -- the game can always use weapon smiths that can clean, repair and upgrade weapons.