I went through this a few years ago and if yours is the switch with the
thermostat control inside the fan knob you can't get it from any dealer.
If it is only the fan switch part that self destructed there is a solution.
You can get a similar AC fan switch for another VW product and change all
the wires over to the new one. You will have to drill a new hole in the dash
and mount it nearby but then you can keep it working just like the origina;
one. I did this a few years ago in Florida so I can't remember all the
details but it was not expensive or difficult to install.

Tony
85 GL Westfailure