I don't remember where I got them, but I have a set of Dura-Ace AX pedal adaptors. The number on the package is "$1399901" then "1S (OCS- D)" if that helps. No I can't explain the "$" but there it is.
And Jim, I have a set of very nice 600 AX pedals (with a spare set of cage plates) if you're interested.
Mark Fulton Redwood City California USA
PS: If you want to upgrade, I also have a NOS Dura-Ace AX crankset and pedals complete with toe clips and clip mounting hardware. (The Dura-Ace AX pedals are narrower than the 600 AX pedals.)