Well the reason for that is a licensing thing. They need rights to make it, but RR won't give them rights. However, I have a Wraith 1:24 model but it's Chinese so it's not actually a RR, but it looks like a RR.
I'd like one also - as a 1:18 scale model! I'm in disbelief that the heavy hitters of the diecast model car industry - Autoart, Maisto, Bburago, Hot Wheels, Frontiart, GT Spirit, Minichamps, Kyosho, Ottomobile (amongst others) - haven't released a 1:18 scale version of this beauty yet.