Honeywell Genetron R134a.
If you want to buy the whole cylinder contact the below mentioned company. They deal in air conditioning and HVAC equipment.
Fakhri Brothers, Plot No. 69-c, 3rd floor, 12th commercial street, Phase II, DHA, Karachi. 111-352-352, +92-21- 32730591-3
Last time I checked a Honeywell 134a cylinder was for about Rs. 13,000.
If you want to buy just enough to gas to fill your car AC, then you will need to check in a market that has car air conditioning workshops. They will have a parts supplier in the area. They might be willing to sell you a few pounds. Just make sure you get it from a Honeywell cylinder.