It's not as easy as it sounds. You can buy the cars and have them exported pretty easily but if you don't have the proper documentation when the car lands in the states it will be crushed. In Australia anyone trying to bring in a car even for storage without the right documents will have it confiscated and crushed. I hear of these horror stories all the time of mint JDM cars getting cubed
Just about everyone with a real RHD car in the US got it in and registered because they know someone either directly or indirectly in the DMV who helped them get it on the road by issuing them with a US legal VIN number. There are other methods too, I hear there are heaps of dodgy Skylines in Florida which are registered as mail delivery vehicles.