apply for retainer certificate, at provincial home secretary office through the DC of your district.
support your application with death certificate and arms license of the deceased, after necessary verification of documents the license book will be endorsed with your photo & cnic number. you may need to mention the number of live cartridges in possession [depending on the class of license ] if those are endorsed over the license book. In 70's the game class gun licenses use to get an annual quota at subsidized price [ read control rate ] drawing of cartridges and same was endorsed over the book licence.
If you have a some friend in police at DSP or higher level he can help you get through the process swiftly.