Hi,
It took me a long time to find one as well, so I am happy to help give you the contact. You can try this place at Fu Tung Market at Tung Chung. They are located at the basement inside the wet/dry market. The name of the shop is Fu Tung Curtain & Bedding Co. at F39. But they don't speak English. It is best you give them the measurements as they charged $300 for coming to do the measurements if you don't end up doing the blinds with them. If you do, then the $300 becomes part of the deposit.