Wust Al Balad - If you don't mind to buy them second hand, there are a few shops in the Balad that sometimes sell them. One is close to Al Quds (the one on the way to Ras al Ain) @Downtown
@Virgin Megastore is cheap, but treat it with care or else it will probably break..Not the best quality. I've seen some @Downtown too, but just make sure you check the quality yourself before you buy!
Fasheh in @Downtown if it's still open. Near Jabal Amman and Shaheen service taxi. Lots of vintage frames, all between 10 and 30 Jd's that are made in Europe.
your best bet is @Downtown (al balad), try Petra St. there's a Marketplace there that sells textiles per meter. (its inside one of the buildings on the right if you're entering from Al-Hussieni Mosque St.) @Souk Al Bokharyyeh