Most of the vendors and retailers who go to Sunday Bazaar operate in various markets throughout the city. If you see something you like but want to scope out his actual store/outlet, you can ask him for his business card/address and go there during the week. Most of them operate in Saddar (I've only asked for books, but all of them seem to operate out of Saddar).
If your question is who are their suppliers, as you would prefer to buy it directly from them, then I honestly don't know.