I just started using Kool Stop Dura Type General Purpose (black) pads in my Ultegra brakes. I think they are definitely superior to the Shimano Dura Ace/Ultegra pads. They are certainly more powerful, modulate better, are less noisy, and seem to keep the rims cleaner and less scratched from debris caught in the pads.
Sorry I'm not sure I have an answer to your actual question. Looks like the Dura Road Holder might be it, you have to get the entire brake holder/pad set, not just replacement pads. Ask your LBS or give Kool Stop's Customer Support a call.
Dave