Honestly, as with any drugs, if you just know anyone who dabbles , you can get them easily.
I don't like drugs personally, but my closest social group has always been heavy drug users during my teens and early twenties (dealing with them is probably why I don't like drugs myself). I've always known where to go get stuff even though I don't partake in that lifestyle myself.
Now when I describe that time in my life to my wife and more straight laced friends, they're surprised because they assume finding drugs or a "shaman" is difficult, or part of some seedy underbelly of society with crimelords etc... But really it's no different than knowing someone who is into any other niche.
Also the idea of a shaman eludes me. Most "shamans" I've met are hucksters. They basically serve the purpose of guiding you in a trip, being a hype person and (assuming an experienced one) knowing how to deal with any issues that arise.
A "shaman" can just as easily be replaced by a good friend at home. Most people just do it for the experience IMHO, but there's nothing special about one.