Hey Steve,

If your goal is to be 100% legal, there's no current option for 400 or 500cc non-chinese bikes I'm aware of...
Honda CB400, 500, Suzuki GS500 are "easy" to find around the Tianma Circuit I guess, but not legally.

I think it will come, as the "leisure riding", as opposed to the "utilitarian motorbike", is growing in big cities like BJ & SH. In the coming 5 years I guess those mid-ranges bikes will become legally available (Honda CBF 600, Kawa ER-6, etc.), but it does not solve your problem...