Back in the 1960s, thumbwheel pots were available in several values.
However the main use was transistor radios, and they all tended to use 5K.
I have not seen any value other than 5K in a thumbwheel in many decades.
If you want to pay to stop the line for a day, run off many-many test samples to get the carbon-ink right, then buy enough good parts to make it worthwhile for the factory, you could get any reasonable value. (25 Ohm or 1Meg may be unreasonable at that size.)
If you find where all the unsold 50K thumb-pots from 1963 were stored and forgotten, then the only problem is they may want you to take ALL of them.
With amplifiers, at some level, you "can" re-design the amplifying circuit to use any pot-value you can get. Sometimes this even leads to a nicer design, though often more expensive.
Trimmer pots can be small and "can" have knobs added. Problem is that a knob-pot is expected to last 5,000++ turns, a trim-pot not even 100 turns. But they are cheap. If you can figure a dead-easy way to replace the trimmer between shows, on the bus from Tulsa to Albuquerque, it may be viable.