I'm faced with the same problem as urs 
A friend of mine recommended style house, Jinnah super. It's situated close to Saeed book bank. I haven't received the suit as yet. Therefore I can't say anything about the standard. But he ceratinly has a good clientele.
Phone #: 051-2650100, 2650572
The best tailor in rwp/isb was Mr. Inayat Shah but he passed away a few years ago. Sadly, When I came to know of him, he was no more.
I came to know of another tailor very recently but he had also passed away last month. His name was Mr. Iftikhar-ud-din of Good Looks, Melody Market, Islamabad.
Let me see if I can find any other one.