Manufacturing laws for MoD products

What are the laws regarding manufacture of weapons-related parts here? I designed a product, primarily for the U.S. market, which I would like to get prototyped, and eventually manufactured, here.

Two problems: (1) these are parts for firearms, and (2) I’ll need some of the related parts in order to do fitting and final development. I won’t need a completed firearm at any time (unless of course the local military wants a demo, in which case I’m sure they’ll supply the guns).

I doubt that anyone here is going to know, but if you know which part of the government I should contact, even that would be a help.

In a related tangent, does anyone know of machine shops which are willing to rent time on a basic milling machine and possibly a lathe? Prototyping will be done in plastic, but the machines need to be accurate, not worn-out clunkers.

Many thanks, M.