>>> The cog, chainwheel and chain do not fit anything else, <<<
I have been told by a friend from Philly that a Sears garage door opener chain can be substituted for the Shimano 10mm-pitch chain with inexpensive success. I have not tried this myself, since I don't own any DuraAce 10-pitch stuff personally. Fred Rehberger has some, though, that he got last year from KMandu on this list.
(I still owe you, Mandu.)
Glenn Jordan - Durham, NC