Originally Posted by sch

Unless the races are truly horrible, you may end up cleaning it up, maybe replacing the balls, using an abrasive pad to clean up the races
and reassembling. The bearing cages are not needed, just convenient to assembly. There are replacement BB for threadless BB housing
that rely on compression, but these assume a certain diameter in the housing, so spacers maybe needed to make them work.

Just a brief google shows this example of such a BB: Mavic Bottom Bracket - Bicycle Parts at discount prices / the Buyer's Guide / Bicycle Parts at their finest! / Professional Bicycle Source / Bike Pro
Availability is another matter, but such do exist.