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.