Yes, you can remove keys on the Kronos 61 easily FYI

[aron]

Like one of the threads said, press firmly on the "back" of the key close to where it pivots. Then slide the key out towards the front of the keyboard.
There's a single spring underneath the key. Now the only hard part is to fix a black key, you need to take out both white keys around it.

Also, getting the spring to go back on the small plastic "pin" underneath the key is little difficult. Use a small screwdriver or something to guide it back. Press down and slide the key back into the keyboard.

I bought keys from Keyboardcountry.com
(Replacement-Keys-for-Korg-M3-Kronos-Hammond-Keyboards)

and partsisparts
https://www.partsisparts.net/catalog/korg-key-m3