can anyone tell me where to get a supercharger for a bike engine from, i see mk's demo rizzla car has a charged gsxr, an extra 70hp on top of the standard 180hp, has anyone been in it?

TTS do a kit so do a couple of others. not cheap though..,

mb customs

BMW mini
Rather big but cheap as chips and hopefully shouldn't be too difficult!!!

Do rotrex do one that small?

Yep - but not cheap - £400 imported...

£400 still sounds crazy cheap for a rotrex!?

The one TTS supplies is a Rotex as far as I'm aware, did you mean £4000?
That is about what I've been quoted for the conversion for my Blade car.
Cheers
Eddie