Eek. $$$$$ I have a full brand new headset, but I'm holding onto it as a spare. This is the 7410 with the cartridge ? Do you just need the fork crown race - i.e. the small disc that slips on the crown ?
I may have an old Ultegra one from a cartridge headset - I will check later - it should be the same part (although not as well finished as DA).