I'm (ever so slightly) ashamed that I must confess to being something of a "headset nut", Derek...
...But that sad fact is probably best left well alone.
Even more sad, I know of no manufacturer of this sort of gear who will provide that type of individual small spare part for any mic or headset.
Nowadays, the standard practice does seem to be exactly as you feared, in that almost everyone requires us to buy the whole item, other than a few who will possibly supply ear pads, transducers and/or entire boom-arm and/or headband assemblies for their more expensive "radio and TV commentary" models.
I'd suggest that the cheapest fix may be for you to take the remaining assembly on an excursion to your local D.Y.I., hardware (USA) or ironmonger (UK) with a view to finding a matching fastener, or one that's possibly able to be adapted to the purpose.
Equally in hope...