You can only import a duty free legal car, it should be brand new and shouldn't exceed 1349cc engine capacity.
It should clearly mention a tag labeled as disabled person car. The only way to avail this waiver is that you go to excise office, they'll fix your appointment with 2 different doctors, they'll examine you and will issue a medical certificate. Then you present it to excise officer along with other docs like your NTN, employment letter, driver's license etc to obtain an NOC. After you obtain that NOC, you'll have to purchase the car as brand new from outside the Pakistan and you can import it duty free. That's your only bet.