For your consideration, Garrett Park Guitars this Fender Volume Pedal FVP-1

The Fender FVP-1 is a passive volume foot pedal designed for guitar, bass, and other instruments. The rocker-style pedal controls volume using a passive 250k potentiometer with a high life cycle for reliable, quiet operation. The tone is maintained at any volume, and the special tone circuit retains high-end clarity as the volume is reduced without becoming dark or muddy.