I agree with magnifico, use taobao.com. It has improved tremendously in the last couple of years. It is still not as user friendly as online sites back home, but now serves a very wider range of product groups in depth.

The other thing that might be worth mentioning is corn flour is found everywhere here. This is not the white corn starch that is called cornflour in the UK, this is ground corn. There are several grades from Polenta like to a fine flour. Google corn flour recipes, and you will find many options from basic breads to cakes.

Coconut flour is another gluten-free option.

Oh, duh. A bit steep, but it'll do. We bought a couple things there and had a good experience.

Regarding corn flour, I'm sure I could make masterpieces, but so many grains are milled in the same facilities I don't know if I could trust it.