Near Guangzhou railway station, there is a big area full of clothes, like Bai ma Yi ma  but these buildings are very expensive. But another market near bai ma, which is in the basement market called DI YI DA DAO.price there is much cheaper, and this market combines factory and retail shops, so if you want to find some factory for order, you can visit there.
Another area is called Shi San Hang.this area is very low price, but very crowdy, and usually only opens until 2 pm, should go there earlier.
If you want to wholesale jeans and if want to find factory, Zeng cheng District have many jean factory and wholesaler market.