Originally Posted by seitenryu
Would the hub ID for the cups/races usually correspond to a cartridge bearing size?
Maybe if you're better att finding a source than I am.
I've done such a rework once, but it required sticking the hub in a lathe first.
If I recall the numbers right Shimano cup OD is something like 29.6 or 29.4 mm, and the closest cartridge bearing I could find was 30.0 mm.
For a front hub there might be a workaround available by going down one size in axle dia, to 8 mm. That'd let you choose a bearing with a smaller OD that could be fitted in place of the cup by the use of a shim or a bushing.
If you have a go at this, remember that (the most common type of) cartridge bearings get unhappy real fast if subjected to an axial load. You have to use an inner sleeve of some sort to take the load generated by clamping the wheel in the dropouts.