I am looking to book the overnight train from amsterdam to interlaken, i'm on the bahn.de site but there is no choice to book the sleeper car? am i missing something?
You'll have to take the City Nighline train from Asmterdam to Basel, and then a regular intercity train to Interlaken. You can book your journey and print your tickets out at home via www.citynightline.ch Make sure you are selecting the direct overnight train from Amsterdam to Basel. You can purchase your Basel-Interlaken ticket once your arrive at the station.
Jigar,
You can book the seats you want, and then call or email Bahn and notify them you want a sleeper car.
I had to do that for my Lake Como/ Munich portion, as I too, wnted a sleeper car.