Sorry to ask the obvious question, but aren't they available from specialist breakers?
Incorrect spelling may be hindering the search for secondhand parts. Not all sites use fuzzy logic in their searches.
I would copy the external spline in steel, make a new adjuster knob from Delrin and wobble-broach the spline into the hole.
I'd just get a smooth bore knob that fits, or bore it out, & shove a grub screw or two through the side to lock it in place.