Seems to be a bit of a rare beastie, I see one on EBay, NEW Campy for $140! 13-24s seem to be available, but not the old "Corncob" 6's, seem to be some Regina and Sachs as well, perhaps PastorBobNLNH and his Freewheel Spa can custom build one for you.
There is a decent 13-21 Dura Ace on Ebay currently, looks nice...but who knows how high it will go
http://www.ebay.com/itm/NOS-Dura-Ace...item27cee47e91