J. Curtis Earl Museum
Decades ago, I knew the late J. Curtis Earl, gun collector extraordinaire -- particularly of NFA arms. I just found a reference to collection, now on display in Boise, Idaho.
When I last visited him, circa 1980, he was still in Phoenix, and showed me some of his pieces. He had a Johnson Light Machine Gun, a Villar-Perosa, which some consider the first submachine gun, and a Soviet sub gun, with a strange and rather garish finish, some parts chrome and some nickel. He'd bought that from a police department, and finally determined that when khrushchev visited the U.S., one of his bodyguards had left it behind in that city (I seem to recall it was Las Vegas). He had two early antitank guns (one is misidentified at the link above as a howitzer) in his back yard. His storage area was a concrete building in his yard, with a bank vault door (salvaged from a bank that was being demolished). Inside were more Thompsons and MG-42s than I could count. He was selling the latter to police departments around the country... he said in those days PDs wanted ANYTHING they could get that was full auto (these were the early days of SWAT), and if all they could get were surplus belt-feds in 7.92mm, that was what they would take.