If you go shopping for keyboard switches, you will find a ton of them listed on Amazon and Ebay. The most common advertised are the 5-pin and 3-pin versions. Both will work on the COMIX-35, however unlike the 5-pin version, the 3-pin version does not have guide posts. The guide posts are essential for proper alignment of the switch on the PCB. If you  use the 3-pin version, you will need to spend a lot of effort to manually place the switch on the PCB and solder it. The 5-pin version "snaps" into the PCB and self aligns, so I recommend you go with the 5-pin version, which I have listed in the parts section...