Bob Marino (http://www.bobmarinosbesttools.com/) announced the other week that he was going to be clearing some old MFS stock. Not sure if he still has them. I actually bought some MFS extensions from overseas after they were discontinued here, but apparently there has been a crackdown on European Festool dealers shipping to the states, even when it's NAINA accessories.
Short of that, you could put a WTB (Want To Buy) ad in the classified section on the FOG. I'm sure there's someone who would be willing to part with theirs for the right price. I know that [member=23629]Daver[/member] had some up recently.