I see that Shimano has part numbers for every washer, nut, and cone in each hub, but these are sold in boxes of count 10.
Is the idea that these (cones, in particular) are consumables and one would use two and keep a stock of eight, or are these meant for dealers, and we need to shop in person rather than online to get just a pair of cones?
It sounds that it's the latter, because when I google the part numbers none of the online stores (consumer stores) show them.
Even more briefly:
Are Shimano cone ten-packs sold to consumers?
Just a raving comment:
Shimano takes the delightful approach of specifying the bolt-equivalent size. Once "M10" is mentioned, you know with certainty that the cone will fit on your axle. Beyond that you might get away with the race being a little off the center, but you're still stuck with the outer diameter for the cone. This seems like a task for ISO.