I would just get a bike turbo, they shouldn't be that hard to find.

smallest turbo I'd have to say.. Check out 85-86 nissan 200SX turbos... Its a t-25 I wanna say.. I've seen donuts bigger than that thing.. its cuter than all hell.. Fisher price my first turbo and ****..

If you know anyone on a college FSAE team, Garrett's giving out turbos that many teams use on their 600cc bike engines for their formula car projects. They're GT-12s and GTV-15s.. The GTV has a VATN exhaust housing that you could probably put the -12 compressor on and have one hell of a bike turbo. Ball bearing and variable exhaust..



http://www.egarrett.com/about_garrett/faq.jsp



Although I suppose you could even buy a new one from them...