EXPAT FAQ
https://www.easyexpat.com/en/faq.htm
I lost my National Insurance Number - UK / London
"I lost my National Insurance Number (NIN) since I was in the UK. Can you give me a new one?"
Yes, we receive some emails like that. The answer is NO, this is a government document.
You must request a reissue to the dedicated administration.
You will find all the information on EasyExpat in the National Insurance Number section.
In addition you can ask/get more information on the forums.