[jan-jaap]

This is awkward though, I have misplaced the key for the Onyx and Challenge.  Does any know what model key it is or have a picture?  Maybe I can get the local locksmith to make one.  If anyone has spares, I'd be willing to buy one.

They are not proprietary and you should have no trouble finding another set. Just google for A126 keys, the originals are made by C&K and you can still buy them. Apparently they were also used in the no-longer used Dutch electronic voting machines