I thought you might find this interesting. It's not necessarily a keyboard but it's a very early "single board computer" or SBC that had a built in keyboard. Previous SBC's had numeric keypads and you entered data in hexidecimal or octal so you only needed 1-9 and A-F plus some other miscellaneous keys.
This is the Ohio Scientific Model 600 known as the "Superboard II" from 1979. You an see the key switches are soldered right to the circuit board so this is not technically a keyboard, I guess. The key switches look like Futaba complicated linear switches?
Here are some pics: