Something about them
I have constant problems with oxidation and a poor connection even with DeOxit on them. The copper has a dull look about it. It depends on what signal you are pushing through them.
It's a primitive switch contact- any high quality rotary ones have silver or gold plating (Brymen, Agilent, 121GW appear gold coloured). Better Fluke multimeters have their own patented switch mech with I think phosphor or nickel plate and more precise, refined fingers. Fluke started out with an off-the-shelf rotary switch in their earlier handhelds.
Some people strip a cheap Harbor Freight $4.99 special and use those, or this guy documented making his own.
https://softsolder.com/2012/09/20/multimeter-range-switch-contacts-whoops/If you can make the rest- the knob/ratchet maybe 3D printed it would be neat.
They are part of a switch which is part of a multimeter. Switch manufacturers only sell the entire switch. I searched but could not find a specific company offering them, which would save tooling and die cost.