I can't speak for Steve, but I "guess" his may have come from the same place originally as mine.
On a record buying trip in the early 90's a mate and I bought literally 100's of Hot Wax, Music Merchant and Invictus "Quality Control" test presses from a guy in Detroit. We didn't know what a lot of them were at the time as many of them only had master numbers or catalogue numbers. We divided them down the middle. I've still got pretty much most of mine and my mate sold them some years later to a well known record dealer. steve may have got his from there. But as I say I don't know for sure.
Phil