Getting unmarried certificate in Pakistan

I am not sure but I think you get one from Kacharey, Model Town, Lahore.
Or Kachery in your city in pakistan.

please share why do you need this certificate,,,,

He needs the certificate to show that he is not presently married and is indeed single.

Just ask someone in Pakistan to do it for you .... suppose to be your father who gotta sign on affidavit paper which appear that you are single.  That paper is just 20 rupees ask them to send the proper document to you by international post. That's all.

If you'll visit pakistan then go with your father to make that affidavit at local district office. Get the legalization from the consular in Pk too.