Make your own content. The world of Shadowrun is very large, and the selection of weapons is large as well. Really all you have to do is
A. Make your own Pistol. It's pretty simple. The hard part is thinking of what it looks like.
B. Make your own weapon mod. Maybe he finds an Ares Predator V with an internal modification that allows it to shoot burst fire, fire a larger caliber bullet, or virtually anything else.
It may not be official Shadowrun canon, but your players will definitely like getting goodies that aren't in the books.