Where do you find the hand crossbow?

If I start with a weapon focus with it, the game crashes when I click on the inventory. So where can I find it? And is possible to dual wield ganster style?

 

They don't exist in the game, that's why it crashes, so you can't use them, let alone dual wield.

 

Better to just use a normal crossbow or get a supply of throwing daggers and make sure you have quick draw.