Hello and thank you for your question. The C190 is designed to work with the Roland DP-2 pedal or the Boss FS-5U pedal.However, any momentary (non-latching) pedal with normally closed switch contacts will work.
You should be able to find the DP-2 at your local music store. It can also be found online at retailers like Guitar Center and Musician's Friend
Another option is a pedal with selectable polarity, like the M-Audio SP2. Because it is switchable, it will also work with any other keyboard you own.
I hope I have satisfactorily answered your question. Please let me know if you need any more information or clarification on this issue.