There are three ways to get your magic mushrooms:
buying, finding and growing.
Buying magic mushrooms
Buying your magic mushrooms is the easiest way, if you know who sells them. Nowadays dried mushrooms are illegal in most countries. Holland and Ireland are one of the few countries where fresh mushrooms are legally sold in smartshops and headshops. The magic mushrooms they sell are mostly the Psilocybe mexicana or the Stropharia cubensis. They mostly sell fresh mushrooms, 25 to 30 grams. If you buy dried mushrooms you'll get 3 to 5 grams. The vendors know the effect of the magic mushrooms and they adjust the portion to that. The portions they sell are normally enough for a strong trip. If it is the first time you use magic mushrooms, the do not take too much. The price you have to pay is about 15 dollars a portion.
If no smartshops exist in your country, you can try the following online shops. Most shops do not sell magic mushrooms to the USA, but they do sell Growkits.
Her you can buy Magic truffles.