First Day Issue Stamps and Letters

I found more than 100 First Day Issue Stamps from 1960's to 1970's when I went thrifting. What fascinating about it was all the envelopes contained letters from "The Foxboro Company" of MA., along an actual signature of a man named Rexford A. Bristol. He was the Chairman, Executive Committee of the company. All the letters were address to certain people at Uniroyal Inc in Baton Rouge, LA. I did some researched and "The Foxboro Company" doesn't exist anymore but it was bought by another company. Alhtough there's no mentioned of Rexford A. Bristol (two sons of Bristol managed the company in the past). Rexford A. Bristol usually talked about the company before he signed his signature. Uniroyal Inc., doesn't exist anymore as well. I wrote an email to the company that bought "The Foxbore" and I am still waiting for a response. All the letters were entertaining because whatever the stamps is all about....Rexford A. Bristol managed to segwey the letter and turned it to a business letter of his own. I just wish I will across someone who really know what I have in my possession. I even thinking about podcasting it or published it as a book like the way it is now.

Does anyone know about things like what I discovered? I find it rare.