Korg sigma keyboard

Hi all. I have got hold of a korg sigma. Its in perfect working condition, but has one major problem. Its missing its keybed. It was a rare French one with an accordion button style keybed fitted.
I am trying to get hold of the standard 37 note keyboard, but its proving very dificult.
Does anyone have any information on this keybed, ie: anyone got one?? Or where to get one,?? Or has anyone got information on how the aftertouch works, and is it possible to use / modify another keybed to fit and work?
The resistor ladder chain is present, so a contact keybed is all I need??
Any help would be appreciated.
Cheers
John

A Moog Source uses the same type of keys, and is 37 notes. But I don’t know where you would find just that keybed, nor do I know whether it will work in the Sigma without some alterations.