It's probably a brass insert that was cast in during the manufacturing process, so of course it wouldn't be something BMW would sell. It's possible a hardware store, Grainger or McMaster Carr would have something similar. Or you might try sourcing one from a junk fairing.
Once you have one in hand, clean the area very well and excavate down to virgin plastic. Epoxy the new one in.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*