Could very well be that the law has changed, but unless it has, anyone with an FFL can do "occasional" importations. It was my understanding--which may be wrong, or the law may have changed--that while those with an import license have to mark their guns, those with just your common, garden variety FFL doing the occasional importation do not.
I have a British 20, clearly imported as a used gun. (It predates the ATF by several decades.) The importer's mark is on the underside of the rib, nicely hidden by the forend. I've seen numerous other guns, imported used, that are similarly marked. Still acceptable? On new guns, my understanding is the same as GrouseGunner's.
