Where do you guys get your frames to build on?

I've been wanting to build my own scooter for a while now from scratch, or pretty close to it. I just don't have the know-how to do a good job welding a frame for it. Where would you guys suggest I get a large, sturdy frame to use as a platform for a super speed-demon scooter? And what's the best combo I could get for speed? 48v, 1000W motor or something like that?? Li/ion batteries? I want speed... dangerous speed. With HUUUUGE brakes of course :D Thanks in advance!