Any sustain pedal with a 6,3mm jack that closes the contact when being pressed should work. Our recommendation is a Fatar/Studiologic VFP1/10. Only use a single pedal, dual pedals won’t work.
Pedals compatible with Fatar, Roland, Moog, Kurzweil, M-Audio should be working as well.
The Korg/Yamaha models may not work though.
Make sure not to press the pedal while you switch on Blofeld.