Most Dealers get thier Guns, Surplus or Not from a Jobber, Like out of shotgun news, Like J & G, Sarco, Century, those Folks Like Century, navy Arms Sarco and all, well they have buyers that go to other countries and on a document call an "End of User Certificate", they would but 1 or all of a countries sell off guns and ammunition, thats what Kept navy Arms in Business for years! Hopes this Helps to some small degree? Nope, I don't do it myself, Just have seen it done in a lot of third world countries! I did a Stint in the Peace Corps!
The U.S.A. is known as a big buyer of suplus guns. So American buyers are not only travelling around finding guns suited for the American market, foreign police and other state agencies are offering their guns to American importers when they decide to arm the force with new guns.
Happened in this country (Denmark) when police decided to change their Walther PPs to H&K pistols. A major change as they went from cal. 7,65mm
(.32 Browning) to 9x19mm (9mm Luger).