A Sine-Cosine output or other Non-linear functions are available with the Non-linear range from Caldaro. The endless Sine-Cosine signal is often used in marine applications, for instance on a rudder, where you need to detect a continuous movement over many full turns.
The potentiometers are of 1-turn type and the resistive element can be either wirewound or conductive plastic. The wirewound offer great stability while the conductive plastic type ensures the best life expectancy.
Sizes from 22 up to 50 mm in diameter are available along with special machining to the shaft and even oil filled types.