I've NEVER seen a green 820 for sale except the one I have. That includes watching eBay for 20+ years, and the big train auction houses.
My green 820 and the 728 Quaker loco both came from a midwest collection Al Levine bought in the 1980s from his TCA news ads. I think it was 1985. No one would pay the crazy prices Al wanted, so they weren't selling. My dad landed the Grace Restaurant account that year and was starting to buy back the trains he'd sold to start the business.
About the photo. . . A freind collects these old pictures. He has kids with their trains, club layouts from the 1930s and newer, collectors at train meets and stores beginning in the 1950s.