Is "Visions of Gray" really a rare item to find? I don't know, I never followed the "zine scene" much.
The magazine was published as a tabloid style publication on inexpensive newsprint paper. Consequently, they tended to wear out quickly if not preseved carefully, and the paper yellows with age. Back issues don't seem to show up very often on eBay (or anywhere else, for that matter!).
I think that explains it somewhat.