Haroon Radio Boatbasin Karachi and Merryland are the best ones you can get in Karachi. The rest have plain vanilla brands. 90% of the shops in Tariq Rd and Saddar carry fake stuff which is hard to recognize ever for picky buyers.
Contact Naeem at Haroon and Hafeez at Merryland. You may give the referral of mine or PW. Yes prices are high but you have the right to negotiate but use that thoroughly. Also they carry legit stuff so you will have to worry less.