As many have said, there were only 10 of them.
It looks like two of them are in service on mass coastal:
http://www.railpictures.net/photo/682302/" onclick="window.open(this.href);return false;
Two more were on SNC and look like scrap:
http://www.railpictures.net/photo/658792/" onclick="window.open(this.href);return false;
That leaves six unaccounted for. Road worthy? Already scrapped? I don't see any reason why MC would sell theirs. They are basically relatively modern superliners that I'd imagine tourists and the RR love.
And there's no source for this rumor? Shocking!
Long story short: this is never, ever going to happen. If it does, MTA will have to overpay to get them back or spend a huge amount of money rebuilding them.