While sake is still a new trend in Amsterdam, there has been a big improvement in availability and selection recently. We are actually at the point where you can get a decent bottle at mainstream liquor stores like Dirk III.
A large part of that improvement is fueled by Dutch Sake Samurai Simon Hofstra and his distribution business Sake Europe. Simon is a specialist in all things Sake and has been doing a great job promoting sake amongst wine stores and restaurants. He has great connections with the sake breweries, an amazing selection (pdf) for Dutch standards, knows a lot about sake and is more than happy to help out with his wealth of knowledge.
I had been looking for a bottle of sake made according to the Yamahai method in Amsterdam for quite a while. When I shot Simon an email he was quick to hook me up with wine store De Gouden Ton where I managed to find a the coveted Yamahai sake!