From what I am told (From a very good source), this is indeed a limited edition kit. I am given the impression variations of this kit will be offered over the next 12 months as the car is developed probably with variations on the TRF501 name.
So I can only presume there will be a spares backup of some kind.
I have seen some spare TRF501X belts on the ebay, so they are beginning to filter through.
Colin