Pretty much all the loopholes that importers were using to import grey market vehicles to the US have been closed, so the only way to bring over a car that has no US equivalent and be able to drive it without any mileage restrictions, you would have to go through the same process for legalizing a vehicle that MotorEx did so they could bring over Skylines, which is a very time-consuming and expensive process.

If you don't mind having a mileage restriction, there are other ways to bring over cars, like classifing them as show or race vehicles.