Choice of material for a cylindrical potentiometer
Consider:


electrically conductive 3d-printing PLA -- you could use it straight, or you could 3d-print the pieces.  It's only "conductive" compared to normal plastic.  It has a resistance of a few ohms per centimetre (but obviously depends entirely on shape)
nichrome wire -- such as often used in (unwound) electric guitar strings, used for heating
various other antistatic protection plastics


A search for conductive plastics found TECAPEEK, which looks like the kind of stuff you're after.