Jan 27, 2015 - 6:17 PM
You can buy it at staffed stations within the region of the pass. Zurich is not in the Bernese Oberland, so I don't expect it to be available there. Since many travelers enter the country there, there might be an exception, but I'm not sure. You can buy it en route to Interlaken in Bern or Lucerne for example. You can also buy it online in the webshop.
The pass includes part of the route to Interlaken. The map shows exactly what's included.
Have a good trip!