There are plenty of guns sold, machine guns haven’t been sold as new since 1986 and have had a special process for purchase since the 1930s.
https://en.m.wikipedia.org/wiki/Firearm_Owners_Protection_Act
See the section on “Ban on new automatic firearms”
Deglazing liquid does not have to be acidic, water works fine too, but you aren’t adding any flavor. It’s the action of adding a liquid to a pan that’s above boiling that works all the fond off the bottom of the pan.