It can be found in a suitcase on the right side of the wall in the Cave of the Abaddon next to Sunflower Summers' skeleton. It is one of the journal entries required to complete the Nostalgia challenge.
I think we did it! We finally convinced the Death Merchants to hear our beautiful Mother Earth's cries! I just had a personal meeting with the base commander, who said they would be taking a long, hard look at our demands and preparing something special for us. I can't wait to see what it is - I bet it's a full nuclear disarmament!