Whenever I speak punjabi, i feed keh main jhoot bol raha hoon. And you did a very much insult of mohtarma machli sahiba by calling her machi. 
Anyways! In Karachi there is dhaba on hasan square (rate is around 600+ per KG). Another dhaba is at nursery bus stop.
And the one and only pomfret fish is sold near city court (never went there) but my colleague brings that whenever we ask him.
Someone (fish guru) told me that whenever u buy fish, always ask for female fish, it is very delicious than male fish. 