The street markets in China (well in Beijing anyway) usually have a fair selection available but I found they were typically poor condition and the sellers wanted too much for them. I never bought any. But you might be lucky so check them out.
Also, if you can find a copy of it, there is a book called Cameras of China by Douglas St Denny which makes a good reference of the different types though it's not totally comprehensive.
What part of China are you going to?