There is a shop called hazari impex on marriot road, ive got a ton of stuff from them, there is also a small office on the 2nd floor of musa market opposite sindh madressah that only deals in a variety of loxeal brand sealants - they are just as good as threebond. you can buy from them.
You just need to look for what you want, there are a ton of shops dealing in many items you might need for working on a car.
While on marriot road look for brake caliper grease, hazari huys had it, also the two shops in plaza selling tools had it, I used to buy plastiguage from them and also a variety of weird stuff.