You will have to check the whole market. Most of the shops on the main road only have Pakistani or Chinese bikes. Most bicycles are with wide (Mountain) wheels, some have the old regular wheels and very few with the slim racing wheels. Also, people don't understand why the bikes should be lightweight. Some shops in the streets have one or two pieces of sports bikes, but the price is of their choice.
I went there over a year ago looking for a lightweight mountain bike(after my 20 years old mountain bike was stolen), but did not find one. The only place where I found bikes that were about the same weight as my old bike is around Duty Free Shop in Blue Area, Islamabad. Unfortunately, Rs.17,000 - 20,000 was way out of my budget. So I settled for the "lightest" bike I could find for 5,800 in Jhuggian, Abbottabad. The same bike was available at Committee Chowk, Rawalpindi, for 5,300.