This Pedal is currently available.
Expression pedal
Korg EXP2 Foot Controller for Midi Keyboard Versatile foot controller/expression pedal can be used with most Korg keyboards, modules and effect processors, when connected to the assignable pedal socket for normal use. It includes an adjustable minimum setting via the side mounted slide control and includes a 3-conductor cable.
Korg EXP-2$49.74
These merchants probably sell this module. Huh?
Korg EXP-2 expression pedal