Procedure of getting Duplicate National Saving Certificate (NSC)
1- Details (NSC Number, Date of Issue and Name of holder) - Photocopy would help
2- File a FIR at nearest police station, stating that you have lost the NSC certificates
3- Police gives you a copy of FIR
4- Go to a NOTARY PUBLIC, get an indemnity bond for issue of duplicate certificate. This will be on Rs 100 non judicial stamp paper.
5- Go to the Post Office, get form NC 29 (also attached herewith), fill it up,
6- Submit all the above documents FIR, Indemnity bond, photocopy of NSC and Form NC 29
7- The post office will issue duplicate certificate.

Keep all the above photocopies with you.

Source - PW.com