Nila gumbad is a good place. You might want to try Fasial Town as well. Their prices are a bit low due to the location. I went there with my cousin about 7-8 months back, and their prices were less. You can bargain down and get yourself a good deal as well.
Also there are some shops on Wahdat Road right before the PU campus intersection. You can also try main blvd, right before the DHA entrance. Shops are located on both sides.
Its good to look at different area markets before making a big purchase. Its a bit time consuming but in the end you will know you got the best deal.