Well, the first seller that I found when looking for the Pilot erasers offered a 5-pack so it will be a while before I run out of erasers.
One interesting tidbit: the plastic guide on the erasers is 0.5 mm wide (I’m guessing they use a standard lead clutch to propel the eraser) meaning that it can be used to clean lead jams (it isn’t as rigid as the usual metal rods but it seemed to work OK in my limited trials).