I suspect that you're incorrect there. While it is an NFA weapon and banned from import, there probably were some who made it in before the assault weapons ban, and which were/are legally transferable to individuals with Class III FFLs.
Or am I mistaken?
You are not mistaken. There are some in these here United States, and if you are lucky they'll even let you shoot it.
Or am I mistaken?
You're *sort of* mistaken. It's unlikely that there are any examples in this country that arrived before the McClure-Volkmer *Firearm Owners Protection Act* the NRA-backed legislation that contained a ban on the possession and transfer of new machineguns by civilians, signed into law by President Reagan on May 19, 1986.
But there ARE exceptions; for those who make MG sales and as *dealer demonstrators* to police, for MG manufacturers, and for certain theatrical and stage weapons portrayals- Hollywood's heroes have to have their leadspreaders.
And it's also reasonably simple to convert the Glock series to full-auto with some internal modification, and quite legal, in some other nations freer than the USA.