With the SCAD code, you can generate a keypad with any number of rows and columns. I've included STLs of a 3x3 example. 

I printed the base and cover in PLA, and the keys in PETG. 

Assembly is pretty straightforward. Run wire through the channels (rows first, then columns), then insert the keys and put the cover on top.

Copper wire (22AWG) seems to work OK but #10 musical wire (or similar spring wire) would probably be better.

The microcontroller in the following video just scans the pins, and displays text corresponding to the first row/column connection it finds.