"debunking" is a rather loaded term, don't you think? I would imagine that you're more likely to pull up crank sites than normal with a search like that.

In any case, there are (claimed) responses from the author of the China study which might be worth reading:

http://www.30bananasaday.com/group/debunkingthechinastudycri...

http://www.vegsource.com/articles2/campbell_china_response.h...

I haven't been able to find these on any "official" site though, so beware ;)