I'm not really familiar with the auction / offroad scene in Karachi...but I'm sure we have plenty of enthusiasts, who can point you in the right direction in the local scene. Alternatively, if you have a particular vehicle in mind...you could always try visiting the threads dedicated to those vehicles, and pose a question there. I know we have a diehard bunch of MUTT fans, and of course Team Unimog is very active on here. Another good option might be to visit the regional offroad clubs near you, and seek advice from them. Off-roaders are notoriously helpful when it comes to assisting others in getting bitten by the bug.
Hum tau doobey hain sanam, tum ko bhi le doobenge!