The U.S. officially imported the Mini only up until around 1970 (that's not an exact date). However, the Mini continued production for almost 30 more years after that. The car continued to evolve a bit during that 30 years.
If you were planning to stock parts in the U.S. you'd base your inventory and offerings on what is supposed to be here.... it would reflect the early cars, not those more common in Europe with fuel injection, ECUs, and security systems. Since it costs money to maintain inventory, it makes no sense for Moss to stock late model parts in the U.S. That's why I expect their U.S. offerings to be only a portion of what they sell in Europe.
Of course, Moss could be targeting the recent owners who have imported late model cars with questionable VIN numbers and pedigrees.