Looks like I have another destination to visit next time I'm in Wisconsin. https://www.tor.com/2021/08/09/dungeons-and-dragons-tsr-museum-hobby-shop-museum-lake-geneva/
I love that cover. I still spend a good amount of time flipping through the various AD&D 1ed. Monster Manuals looking at the art.
be prepared to part with some cash :-)
You also might want to swing by Stockbridge, Massachusetts where the Holmes Basic Set Cover painting is currently on display.