When in A’dam you can stay by the “Doria Hotel”, just off from the Dam. It is not so expensive, and you can get Kosher Breakfast there.
When I was there, it was a last minute booking, and I was told, that due to last minute booking, there wouldn’t be Kosher food until my 2nd morning there, but when I came down the 1st morning, they had come up, with Kosher food.
NIK is website of the Dutch Rabbinate. There is a Kashrus listing there, amongst other things.