Argo chronicled his importation efforts.
There are/were provisions for individuals to import a shotgun on their own.
If a person were interested in doing so, and wasn’t stationed in Turkey, it would behoove the prospective importer to study the chain of custody requirements for an individual import.
The area that provokes greatest anxiety for me, is what happens to the firearm after it is handed to the freight forwarder. Sometimes these activities seem to go dark for great lengths of time provoking anxiety.
There are American retail gun companies importing from Turkish manufacturing companies that do enough business that for a fee, your custom gun could probably hitch a ride stateside.
I highly recommend searching for, and then reading Argo’s story.