The only viable option that I know is to use 23 position rotary switches with a stop pin at 18 positions, and add new overlays on the panel. 18 position switches are essentially impossible to find.
Blore Edwards do them - the PZ range. You buy the wafers and mechanism separately (you can even select the rotation torque). 2A rated contacts.
https://www.blore-ed.com/product-page/pz-wafer-kit
They are the right diameter to fit.
Craig