Why dont you just go to all the coffee shops you can find, and buy the max amount from each. Thats the only way you can get it without buying from a dealer, and unless you know any, i dont think you'll be able to find a dealer in holland that will sell you a key.

You might aswell find a gang on dealers in downtown parts of cities, and arrange to buy a kilo... but what do you want with a kilo? You do realise that is 36 ounces. Thats a hell of alot.