This is probably of no help to any of you, but I recently bought a Twilight Zone from a collector/restorer in the UK who has 2 Alien machines (standard I believe). I got to play on it and agree with what has been said already about it being a very impressive machine. At the time of playing it, and until finding this thread by chance this morning, I had no idea of the scale of the issues in acquiring one.
He is selling them (he tried to sell one to me) but unfortunately as far as I know the UK price for these pins new was higher than the US one, and shipping would of course be prohibitively expensive. It could be an option if someone is desperately after an Alien pin with the cost being a secondary concern. Obviously parts / support would still be an issue in any event.
EDIT: Seems he listed one previously on Ebay at £7995, which is a serious amount of dollars and presumably many thousands more than you guys would've paid new.