There was some interest in this topic particularly from our friends outside Karachi. Following is some more info and my views on the market.
I discovered the Sunday market as a child just passing by one Friday around 1986. It used to be a Friday market then and held at a slightly different location. At the time I was interested in keeping chickens & Budgies. Every few weeks I would ask my father to take me there. It felt like a visit to the zoo.
I believe that the Sunday market has played a very important in the development of the bird keeping hobby in Karachi. It is a place for hobbyists, small breeders, commercial breeders, margin traders and shopkeepers to come together and trade in a free market. Small breeders benefit by cutting out the middle man and selling directly to hobbyists, for the hobbyist it is a source of good birds directly from the breeder at a reasonable price, for exporters this is great place to fill their orders. The market also caters to the other needs of the visitors. You will find cages, food and water containers, clay pots, bird seeds, loucern, corn etc
In the market you will find all varieties of budgies, cockatiels, lovebirds, pigeons, green ringneccks, desi chickens, finches, doves and even goats and aquaruium fish.
The market has its limitations though.
You will not find the more expensive varieties like ringneck mutations, greys, Eclectus Cockatoos etc there. Although occasionally there will be some one there with a bird or two it is not the place to get these birds.
The market has no official status with the city administration. To them it is a nuisance. It is not well organised. Currently it is held on the side of a bridge and in crowded streets. When the city administration clamps down it shifts to another location a block or two away.
You need to beware of your wallet. You could lose it in the crowd if you are not careful.
I believe that every major city should have a weekly market like this. I don't know how it all started in Karachi but with a little work it could also be organised in other cities. It is just a matter of putting the seed in the ground and getting the word around.
I would request the Karachi friends to post some pictures of the market if they have any. If not I will take some the next time I visit and post on this thread.