:dft012:There is a fellow (randymofoco) selling new VW bus brake master cylinders on ebay (item #8001455641) for about $25. They are 211-611-011J which matches the part number from the Amphicar Interchange List.
Ted, You have to pay attention to the diameter size and the depth of the hole that the rod from your pedal fits in. You can use the VW cylinder you may have to modify the rod. I have been using the VW master cylinder for about 5 years now. I also use the same cylinder on my racecar.