That is the actual keyboard!
I have made a preliminary design using standard momentary contact switches (the OMRON 6 mm x 6 mm type with a 2.3 mm shaft). It would fit between 3 mm plywood sheets as shown here:
The pink cap would be 3 mm plywood as well (engraved with the symbol on the top and drilled on the bottom for press fit).
The preliminary CNC design is presented here:
A preliminary PCB
Here is the preliminary PCB:
The preliminary PCB does not include any the logic components. Looking at this board, all the electronics should me moved to the top of the PCB.
I am considering the use of these switches (12 mm x 12 mm) as they have a cap built in:
I should be able to engrave (CNC) the symbols and perhaps fill with black ink the engraving strokes directly on the cap. Alternatively a laser engraver may work here.