I think the only keys that are "almost" compatible with the Emax/Emax-II are the ones from the Siel DK80.
But even then minor changes must be applied...
...at least that's what stated by the guy from whom I'm buying synth parts from time to time.
Here's a link to his (dutch) website where you can buy the Siel keys and where is shortly explained how to apply the changes - but I'm sure he will explain in more detail if you send him an e-mail. He helped me very well in the past when I needed help to replace some of my Matrix6 keys.
Link:
http://www.vintageplanet.nl/PS: I have not tried those Siel keys myself yet.