My best guess, after looking through the WIKI section would be ALPS rubberdome. The one depicted in the ALPS WIKI has a white stem though.
Does anyone have more info on these?
The device is a Sharp PA-3100DM electrical typewriter btw. The keys feel pretty nice - light and slightly tactile.
Keycaps are ALPS compatible (the white one on the right is from my Minitouch, the other two from the typewriter).
