I don't understand why there isn't a Mame page filled in by people like yourself on the last known whereabouts of rare arcade machines. For example, you know who won the auctions, etc., and maybe more info on those collectors such as contact details or websites are known. Others also remember where they last saw games that haven't been seen since.
At least if there is a knowledge base of who has what, then one day when a Mame friendly person with a lot of money comes along, or when one of the collectors dies or goes bankrupt, we know where to buy the game.
For example, I remember reading about 2 protos in existence of a rare military game. A mame friendly person got one, and I think it was dumped. Anyway, suddenly another user posts about how he remembers seeing it when he was a young man. He'd seen the 2nd one which no one had ever seen but had only read about. Immediately, they asked where he saw it. I think he said in a hotel for a military recruitment day, or in a recruitment centre. The point is, obviously that hotel or place could have been contacted by one of us, questions asked, maybe a number gathered of the manager from the day, more calls, etc., then the knowledge of where the 2nd machine is.
I'd love to see Bouncer from the Ninja 3 film. Surely someone alive knows where it is. Maybe the actors have DB profiles or something.