Well, Russian SKS rifles were imported in bulk with importer marks by the boatload. But like your Nagant revolver, that is how most got to the USA in more recent post 1968 times. Different story with most of the collector Lugers, other than VOPO's and 70's Mausers.
In fact when they brought boat loads of Chinese SKS rifles of Vietnam vintage into the USA a few years back, it had a negative effect on those Vet bring back SKS's that were already here. Why? Because they brought in so many at once, that numerous SKS's were not stamped with the importer as they were supposed to be. The importers and distributors caught on to this and culled out all the unmarked SKS rifles. So now, it is only certain to be a Vet bring back SKS if you have the GI bring back paper. This lowered the value of Vet bring backs that don't have papers. I know, because I acquired two SKS Vet bring backs long before the mass importation. But I have no papers.
One was even captured unissued! I bought it from the Marine who took it out of the crate after they hit an enemy convoy.