So you are certain the switch isn't functional? Did you still check the 15A Stop fuse in the Fuse Box and make sure its good?
The switch can be checked with a Multi-meter/Ohm meter to see if its functional.
The Switch itself suppose to be Normally Closed. This means when the Brake pedal is not in contact with the switch the contact is closed and the brake lights illuminate. When the pedal makes contact with the switch, it is in open state and no light emitted.
I would suggest take out the switch and carry it in the bamboo/parts places and see if you can work up a substitute.
There are people who are scrapping these Vans around. Try Fastrac by Nagar Site or Neck in Princess Town.
Ebay has, about $500 Landed,
If you would like further info on the wiring I attached a wiring diagram. Have fun!