Welcome to here. There are many, many Chinese-based members here who can guide you bikes, routes, and most anything else dealing with China.

I like this recent thread about riding to Mt. Everest. Besides the rider who is writing the thread and his friend, who hired a guide, they meet up with a tour company run by an Austrian ex-pat who also runs tours to Mt. Everest. Read it and see the contact info to the tour company...might be perfect for few weeks' ride...

http://www.mychinamoto.com/forums/sh...-Mount-Everest

or this ride which seems to have more adventure on a different route...

http://www.mychinamoto.com/forums/sh...m-with-no-plan

Have fun, but be safe! China seems like it can be unforgiving!!