I am quite sure I have to buy this in switzerland- but can I get it at train stations outside of the B O (ZRH or
Lucerne?) or do I need to get it in Lauterbrunnen where we will be staying?
You should be able to buy it in Luzern, and that town is actually on the network covered by the pass (it covers 50% from Luzern to the stop just before Ballenberg, near Brienz---I can't read it on the map):
http://www.regiopass-berneroberland.ch/images/karte_gross_dfe.gif
The rest of the trip from there to Lauterbrunnen or wherever your hotel is would be covered 100% if you want to count this as one of your 3 full covereage days on the pass.
Lola thanks- that also would mean that some boat trips in Lucerne would be 1/2 off too?