Cardboard Expression Pedal DIY MIDI Controller for iPhone - Hackster.io
Beat Bars EX2M Exp. Pedal -> MIDI USB Adapter | MUSIC STORE professional
MIDI Expression Pedal EX3. Programmable and configurable. An autonomous MIDI expression pedal for sending CC events (e.g. Volume or Modulation), Pitch Bend or Aftertouch. : Amazon.co.uk: Musical Instruments & DJ