I think the foot switch is pretty much a standard item for older American cars. You might be able to get a new one more easily than you would have thought.

Another possibility is to go Euro--the foot switch was only used on USA models--and have the turn signal switch also control high/low beam. It may be that you can do this with your existing column switch by adding a relay. If I recall correctly, the high beam flash function was disabled on USA cars, but can be obtained fairly easily. This would probably be a first step to converting the switch. Perhaps someone else can remember the details of doing this better than I do (It's been a while since I had a 122)