Imran, there is a place which sells imported quad bikes, in Rawalpindi.
Let me warn you, first off...the quads which he sells are imported AS SCRAP from the UAE, Japan, etc...so they are NOT necessarily in good condition, so you MUST bargain HARD for anything that you do like. You would be lucky to find a good piece, although I found MY quad bike (which is a 350cc, 4wd, high-low range Suzuki Quad King) from there.
This place is located at Committee Chowk. If you are traveling from Liaqat Bagh towards Committee Chowk...do NOT take the underpass, and instead, stay on the left side road. The shop (which sells bikes and quads and trikes) is located just short of the main Chowk. You'll be able to find an assortment of quads over there...ranging from kiddie quads to big boys' toys. Prices range from Rs 25K to Rs 250K.
Best of luck.