Indexed headset - repair or replace?

OK, finally got around to dis-assembling my headset.

Cartridge bearing in the bottom looks fine, maybe a bit wobbly.

The cartridge bearing in the top came apart in my hands. It seems to have failed. I have all the balls and the cage separated in my hands. Is this unusual?

So I need a replacement cartridge set for a Shimano Pro RM-01. They are stamped Tange Seki. Any ideas where to find such a thing for sale?

Yes, very unusual. Normally when headsets fail, all the balls fall out and roll underneath the sofa. You've done well to capture them early...