I am a part time translator in a shipping company in Guangzhou. I always take the foreigners to the wholesales markets and help them with shopping .I often provide some information of Chinese products after they back to their countries, so I think I am very familiar with most of the wholesales markets all around of Guangzhou.

There are some large and well known clothing factories in Guangdong provinces, Most of them are located in the cities such as Guangzhou, Huizhou, Foshan, Meizhou and Shaoguan .I have visited some of them with foreigners .there are so many clothing wholesales market in Guangdong, I suggest you to come to Guangzhou and see the every thing by yourself, so that you can get an idea about the fabrics or companies in Guangdong.

It is hard to say the minimum quantity, because it is different from person to person and it depends on what kinds of clothes do you want to buy. Generally they may ask you to buy more than 10 items of clothing in order to share the wholesales price.
Generally they don’t provide the shipping service for you ,yet there are few of them will do that if you can establish a good relationship with them, simultaneously, you can ask an agent to help you or ask the shipping companies take away them from the shops.

Good luck!