First try to give 12 volt directly to the blower motor and check if the air flow has increased (you can do it at your home only a piece of wire is required) if not then get a new blower motor and replace it with the old one temporarily and check the air flow again, if still it hasn't improved then it indicates that the evaporator fins are clogged with debris that your car has collected in the past 14-15 years and the blower has forced them through the evaporator. It is better to disconnect the evaporator and remove it from the car for inspection, either replace it with a new one or use the old one if you think it can be cleaned easily.
In Rawalpindi you can go to chah sultan, glass factory road there is a guy Faqir Muhammad he has a lot of such stuff in his warehouse.