What's size are we talking about here? Try Teemall. Check out the top floor of this mall. It's kinda like a factory store of different brands of shoes (and clothes). 

Every time I have needed shoes I have found them, even in Guangzhou.

I wear a size 13, quite large feet even for western standards.  Normally here, shoe stores will display the "regular" sizes they sell most, but if you ask them for bigger sizes, I have found that they some carry them on their warehouse.

I found a pair of brown moccasins and also good leather men's boots at a Guangzhou store located on the street close to traffic and only pedestrians allowed.  The moccasins were 199 Rmb, discounted to 160 because they had them long and no sale.  The black leather boots went for 299 down to 230 for the same reason.  The saleslady kept on bringing large size shoes out, but I had enough with those two pairs. 

The mall at the end off what they call Up Down street, it has a KFC and Pizza hut in the front, at the back down stairs you will find the jade market, in between the front and the back is a whole bunch of cool little stores that have just about everything in big sizes. just wander around the little allies on the bottom floor there you will be amased at what you can find.