with a little, OK lot of work on your part, you might be able to get something to work. This
https://www.sparkfun.com/products/9117 is a 12 pulse grey code encoder. 12 is nonetheless better than 24 or 24 or 1024., but it;s not the signals you want.
If you combine it with the 402 here
https://www.elmelectronics.com/ebench.html#RotaryDecoders you'd get awfully close.
If you divided the outputs by 2 which is easy to do with a Flip flop your even better,
One of the problems is I, or you would need to know the voltages "across the switch" when it's in the open position.
When you know the voltage, I have another test based on using a few diodes.
If you could reverse engineer anything around the switch, that would help. It could be pulled up through a resistor to +5, +12 or any voltage for that matter. That would help with the interfacing.
Three major parts at this point: encoder, encoder to UP & DOWN and probably a ULN2003. You'll need a 5V supply somewhere or need to be able to make one from whatever is available DC-DC converter.
It might be fun. Maybe not cheap and definitely not mechanical.