In most bigger book shops or department stores you can buy books on origami. Because it used to be very hard for me to get different kind of books in the Netherlands, I bought my origami books mostly on holiday abroad. Luckily, today we can buy a lot of origami books via bol.com. When I’m bored I’ll browse through all the origami books they sell and mark all the books I would like to buy some day… Don’t forget to search in both the databases of Dutch and English books to find a lot of books. The shipping costs for orders via Bol.com are very low (€1,95 per order).
Most (Dutch) (old) origami books are available on Marktplaats. You can buy them second hand from people. I would recommand these books for beginners, because there are filled mostly with easy diagrams. Although I personally don’t like most of these books, because the diagrams are too easy, I can recommand the books of Everdien Tiggelaar. She has written origami books about boxes, kusudama, geisha’s, etc. I own about 10 of her books. Every now and then someone sells Japanese or English origami books or old copies of Orison (Dutch magazine of the Origami Society Netherlands). I bought over 10 (mostly Japanese) origami books via Marktplaats and I have had very good experience with it.
A website to buy Japanese origami books online is Yesasia.com. I don’t have any experience with this particular website, but they do have a lot of Japanese origami books. If you order enough, the shipping costs to the Netherlands are free.