In the Netherlands, access to psilocybin depends on the form and its legal status.
Magic truffles are legal to buy and possess, and are widely sold in smartshops and online. They contain the same active compounds as psilocybin mushrooms, and products vary in potency.
Mushroom grow kits are legal to purchase, but once mushrooms grow, possessing them is illegal under the Dutch Opium Act. Enforcement often focuses on trade, yet distributing or selling mushrooms can lead to prosecution.
Isolated psilocybin in powders, capsules, or extracts is illegal. Only licensed institutions may use it for research with a special permit. For a concise overview, see this Q&A on psilocybin in the Netherlands.
Hope this helps. Stay within the law.