rotary encoder, got a 20ppr but need more like 200 ppr
It may be a better idea to emulate the rotary encoder with a microcontroller, a potentiometer, and a couple of small solid state relays or optoisolators.  Generally a rotary encoder presents two SPST switch closure contacts that will output a quadrature waveform.  It would be relatively simple to map ADC readings of the voltage off of the center tap of a pot into a quadrature encoder signal with an arbitrary number of pulses per rotation so you can better match the range of the pedal to the range required by the drum machine.