Need Help Finding Deceased Grandfather’s Shareholder Information? Northrop Grumman

Shot in the dark here.. My grandfather worked for and retired from Grumman, now Northrop Grumman. He passed away back in 1998. My family and I know that he had shares in the company from his time there. Shortly after he passed I even saw the documents supporting this. Unfortunately over the years, these documents have been misplaced. I have turned the family home upside down looking for them. What are my options, if any, to look into his shareholder status and any shares he owned? I’ve searched