I regularly buy parts from Czone (
https://www.czone.com.pk/) located in Gulshan-e-Iqbal near Nipa Chowrangi. The store sells computer items in excellent condition. The last item I bought was a 2TB Portable HD from the store for just 14k in March this year.
PakLap (
https://www.paklap.pk) is also a reliable retailer.
I bought my laptop from the store located in Gulshan last year at a reasonable price (2.1lacs). It's best to visit the shop to buy parts, as they can get damaged during transport.
Address
Gulshan-e-Iqbal: B-4, 2nd Floor, Momin Square, Block-6, Gulshan-e-Iqbal Karachi-Pakistan.
Saddar: GB-11 TECHNO CITY MALL OFF II CHUNDRIGAR ROAD, KARACHI, Karachi, Sindh, Pakistan