Impactguns.com is one well known dealer of ATF regulated machineguns and AOWs [0, 1]. Based in UT if memory serves. Be prepared to drop 10k USD+ And obviously the bg check / atf stamps etc. and any fees your local receiving federally licensed firearms dealer may add.
I have zero affiliation with this site, they just have a large, dynamic inventory so it makes for fun browsing for me.