I bought wood dowels that were inoculated with them from online, and had a maple tree that needed cutting down in my yard. the wood should be harvested in the fall as soon as the tree loses it's leaves so it's packed full of nutrients and energy it'll need for the spring; takes a lot of energy to make leaves and buds and seeds. you will get many more mushrooms doing that. then scrub the wood to get all the dirt/lichens off of it(don't want any potential breeding places for bugs or anything sucking nutrients from them). then in a honeycomb pattern drill holes in the log and hammer(rubber) the dowels in, afterward paint on some melted cheese wax to seal any freshly cut face of the wood and the exposed end of every dowel; this makes sure nothing else but your mushrooms colonizes the log so it's very important. also, do not damage the bark! it is the most important part of the log, and will no longer fruit mushrooms if it comes off. water the logs about once a week for an hour or so, the goal is to keep the wood between 30-50% humidity. keep them in full shade and out of the wind, they will produce mushrooms anywhere between 3-7 years depending on the size of the log and how well they're taken care of. when one of your logs starts to breakdown and is no longer producing mushrooms, drill holes in some new logs, shred the old ones, and pack the holes in the new log with the shredded old log, you'll never have to pay for mushroom plugs again! just make sure everything you use is sterile. some people prefer to bury their logs halfway in the dirt, it helps to keep the humidity up and less chance of them drying out.
Strange tip! shiitake logs like to be flipped over and beaten with a rubber hammer, it plucks their mycellium like a harp chord and sticks it to new wood fiber, giving them a boost of nutrients and promotes colonization.