Sounds like an amazing adventure!
I would agree with the above post in some respects. An important part will be key components like a rack. It´s worth getting a decent one (having bought a crap one and travelled 12,000km rewelding it together 8 times I definitely know about this one).
A high range of gears may be advisable, but I´m not too sure on availability of things like that in China - surely that´s where the majority of these pieces get made, but not sure on local availability . And you´ll be wanting the best best best gear ratio you can find for that trip.
As for frames etc, I´d say you could probably find what you need there. Frame schmame. I have only seen rare cases of cracked frames. Never bought a new frame and I´ve done fine. Mind you, I´ve never spent over $100.00 for a second hand bicycle, and they´ve all served me just fine.
It might be worth getting in contact with a local bicycle club or even just a local to find out what sort of stuff is out there at the moment. Be imaginative and use sites like warmshowers or couchsurfing to broaden your network.
Like I said, sounds like a wicked adventure. You´ll have an absolute blast.
A buddy of mine who traveled overland through Tibet by bicycle says he hasn´t cycled in a place that has had even a similar effect on him.
Good luck and ride safe!