Ordering magic mushroom spores is legal throughout most the United States except in Idaho, California, Georgia. This is because it is only the psychoactive substance (4-ACO-DMT) that is inside of mushrooms that is illegal. However they are strictly sold for microscopic purposes and growing even the mycelium can bring about a cultivation charge if caught.
While sold for microscopic studies more then likely most sales go to those wishing to cultivate the mushrooms. Growing mushrooms is very easy as long as you follow proper procedure and maintain a very sterile environment. However growing magic mushrooms can result in a prison sentence of 1-20 years in prison depending on the state, and the amount being grown.
However in many states you can find them growing wild, specifically in humid, high temperature areas. They can normally be found growing in cow and horse, dung. Sometimes you can also find them in colder environments growing on wood. Picking these wild mushrooms though can have terrible consequences, there are many mushrooms that look like psychedelic mushrooms that are extremely toxic and can cause everything from extreme nausea to death.
Some of the common states where they are found are Southern California, Florida, and Texas. They can be found in much of the southern United States but previous states mentioned are where they grow more most commonly. They can normally be spotted a few days after rainfall in the spring, summer, and sometimes fall. The evaporation of water off of mycelium encourages the growth of the fruiting bodies.
Hunting for psychedelic mushrooms on private property can be very dangerous. You can be attacked by wild animals. Possibly shot by the property owners. Or arrested for trespassing and possession of magic mushrooms.