Ball races use balls and people have suggested making tail-less Prince Rupert spheres for use as bearing balls.
There are also such things as roller bearings, where the ends are obviously not round because they roll in a cylindrical way not in a bally way.
Hence the obvious solution is to mount
Prince Rupert Drops in such a way as they are constrained to rotate round the long axis of the tail. That way the bearing pressure is always on the strong rounded sides of the drop.
The mount has to protect the tail not touching it of course. Presumably the mount would be shaped around the base of the tail at the inflection point between drop head and tail.