I think it's possible the older one may have been replaced by the present FSB due to some finish removed from the barrel. I've removed taper pins on a couple barrels a while ago and understand it would take a lot of luck for sure to find one first then fit it properly.
The next crazy idea is to find a way to replicate an M7 Green Handle Bayonet. Original handles look like plastic or possible finished stacked leather. Maybe it might be possible to use M1Carbine Bayonet handle somehow if it fit...(?) GB had an original that "ended" at $1900 plus $50 shipping... shucks, just missed it.
It's apparent I must be obsessed ~