I built some wheels out of used Ultegra 6600 hubs, and both front cones are pitted. 6500 and 6600 are the same cones, including the dust shields. But some things online imply that the 6400 and 5500 cones are the same as these, and you just would need to move the dust covers over.

Anyone had any experience finding replacements? The part number for the cones with dust covers is Y24W98090. Wheels Manufacturing sells 5500 cones (which cost more than this hub did).

I feel like a lot of stuff from this era was more compatible than not.

I've done plenty of finding replacement cones for various hubs, though my memory is a little fuzzy on whether or not I've specifically used 6400 front cones on a 6600 hub. I'd generally say that with Shimano cones, if the bearing surface is the same shape and size, and the spot where the dust cap sits on the cone is the same diameter and located in the same spot relative to the bearing surface, then you can usually make it work. Minor differences in the length of the cones can be compensated for by removing or adding washers between the cone and locknut.

Looks like it doesn't have HB-6400, but I found this chart that could be helpful for future cone searches.

Andy- I think I have what would work for one cone. I have a new 6500 ft cone w/ dust cap. Here's a few shots. Sorry just the one. Let me know if you want it, $7.00 plus shipping. Andy

Thank you! The only problem with this chart is that the actual cone is shared more widely than the cone + dust cover assembly reflected by the part numbers. But that is an excellent reference.

Excellent, Andy. I'll see what I can find locally and get back to you. Thanks.

I just found this thread which discusses some of this:
Shimano hub cones

You probably already knew this, but just in case (and for the benefit of other readers):
When you re-assemble, leave a tiny bit of play. When they're adjusted correctly, they will last indefinitely. Most people unfortunately fail to realize that the axle is slightly compressible, and when you squeeze the skewer down, you press the cones toward each other, putting a lot of pressure on the bearings. When they're properly adjusted, there will be slight play in them when the wheel is out of the bike, and that play will just barely disappear when you install the wheel and squeeze the skewer lever down. The grease won't even turn dark. The last time I had one of my Ultegra hubs open, it had 40,000 miles on the original Shimano grease, and it was still that bright yellowish-green color, and transparent.

I found a used 5500 hub with the same (though unmarked) dust caps and good condition cones. So I think I'm good. Thanks, again, Andy!