I was told by a dealer that it was a TVR part only. But then I was told the same thing about the wipers and the motors off a mini! Just with a different drive gear and worm gear.
I'm 99% certain its a TVR special and they are quite rare. I actually got mine from Henley Heritage last year as my normal sources had been waiting quite a while for the factory to send some.
Ordered one from David Geralds just recently for my S2, arrived within 2 days as he keeps them in stock. Forgotten the price as i got a new otter switch at the same time.