As Jim mentioned a Marti report may provide some clues. In general export cars could have been sold to to military members through the PX or ones sent to dealers in specific regions or countries.
A few places to look for clues.
1- Your buck tag. These often include the country where the car was suppose to be going to
2- Country ID plates. In many countries they attached their own VIN plates after cars passed inspections, certification or modifications needed for that particular country
3- Owners manual or other factory paper work. Owners manuals were available in a number of different languages and are often filled out with the original owners name or other information that may provide a clue.
4- Check out the interior (under seats, carpet, ......) for clues. Match books, receipts and so on may provide something to go on
5- Since you didn't mention that the car carried any T5 emblems were can likely eliminate that possibility. These were a fairly small number of cars sold to Germany because of a naming issue with the MUSTANG
That's a start - good luck