Any suggestions where I might find one?
Below is one for a 1971 220 on ebay, but the number stamped on it (923) is different from the "825" on mine, suggesting incompatibility. They sure look the same, though.

http://www.ebay.com/itm/NOS-Bosch-Mercedes-220-w115-Distributor-vacuum-advance-unit-0001582718-923-M115-/

I'd prefer a single port version, as my emission controls are incomplete/disconnected.