SGC I think right off on Tariq Road, dont really remember, there are like a whole couple of rows of streets just full of men's clothing shops, most of them called Kurta this or Kurta that. If you ask any guy in KHI Im sure he will know for sure where exactly it is. I found some really nice stuff there and its convenient because all the shops are lined up right next to each other so if you are picky and need to see a million things before deciding, its all right there. Junaid Jamshed's boutique is there as well. His prices are very decent compared to other designer shops. I like the design you picked, its exactly as a sherwani should be -simple, elegant and classy. Just hate some of gawdy, tacky stuff some people choose, all these horrible clothes with bold, flashy kaam on them! barf
It's called "kurta galli" and if I'm not mistaken it's in the galli behind Chawla Centre. There are tons of shops there - most will do custom orders - though my experience has only been for shalwar kameez rather than sherwanis. Junaid Jamshaid has a store in that area if you want to check them out as well.