I was playing with the innards of the BB (see thread below) and noticed
that it's simply a splindle, two machined cups, a spacer and two
standard 6002-RS [1] cartridge bearings, all simply held in place by the
compression of the cups. A quick Google reveals that these can be had
for a mere 3.41UKP each from a motorcycle parts store - get two new ones
and the BB is as good as new. The BB is branded "PowerPro" and I think
it's an FSA product.

Why can't Shimano do this? It's not as if their BBs are unusually
long-lived - I destroyed my last UN72 in only about 2,500 miles of road use.

Anyway, the replacement, should the RH cup ever come out, is a TA Axix
which also uses replaceable standard cartridges.

[1] you'd think they'd use 6002-2RS for a bicycle but, to be fair, it's
a track bike and isn't supposed to go outside much.