Mace Security International sells a weapons poster/chart. It is not a form for your staff, but it illustrates the different types of firearms they may encounter. Their phone number is 802-447-1503 or, if you're not in Vermont, 800-255-2634.
I have not personally purchased anything from them, so this is not an endorsement of their products. They sell a variety of security-related materials, some of which may also be available elsewhere. I'm sorry you're in a position where your people need to be able to identify weapons. We can't pay them enough for that kind of duty.
_________________________
Opinions may not be shared by my employer. Advice is worth precisely what you paid for it.