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.