Quad project engine needed

Hi folks, hope I've posted in the right place.

I've a Chinese quad at home with a 4stroke 150cc engine. I've recently began work it. Removed the full engine, scrape down metal work and extra welding on all joint points. Now I need to replace the engine. I'm hoping to find an engine for it. Sized from a minimum 200cc two stroke or 400cc four stroke. Maximum sized 1000cc. My ideal engine would be a cbr600 or similar size. The actual dimensions of the engine aren't that important as the quad can be modified. Does anyone have an engine or know where I could get my hands on one. Thanks in advance