Vlieger Papier is my top of mind choice when I need to buy calligraphy or drawing supplies…read more Upstairs they have a great collection of pens (parallel pens, brush pens, line art pens), pencils and everything you can imagine. Their notebook selection is also amazing, you can find pretty much any kind of artistic (plain sheets, these one with black covers - wired or not -, some other brands like Moleskine, etc) or note taking books (there was a day I saw a music sheet notebook too, so there's a lot of options) in different sizes.
Some people say things are expensive there, but if you compare to some online stores in the Netherlands, it's the same price (at least for some calligraphy supplies; can't say about the rest).
But you can also find "basic"/common stuff, like drawing pencils, erasers, rulers, these kind of things.
If you're more into painting and crafts, you will find a lot of options in the main floor. They also have nice classy envelopes,.