I'm in CN these daya and haven't found a folder specific shop. I did see one on the web in Tianjin, and they carried Birdy and CarryMe ... but at import (taxed) prices.
There are low cost local brand bikes everywhere, which are very very inexpensive but probably won't interest you.
There are also many Dahon dealers, who carry imported bikes (at foreign prices) as well as the unique to CN Dahon models, and there are one or two that might be of interest.
http://www.dahon.com.cn/
Pacific TW (OEM for Birdy, Reach, CarryMe etc) list 12 CN delaers, and these shops might be worth a visit:
http://www.hometec.com.tw/shop.asp?sc1=3
There are also one or two decent Oyama bikes (FBI series).
http://www.oyama.cn/index2.asp