I posted about how to propagate our fungal friends a little while ago in a thread about building soil with woodchips.

make mushroom slurry to jumpstart decay and soil building. Collect whatever random mushrooms you can find. Wear gloves if mushrooms in the area can be poisonous to touch. Collect buckets of rainwater/pond water/no chlorinated water (or leave chlorinated water outside for a couple days, or boil/carbon filter water treated with chloramine). Blend mushrooms with rainwater into a grey/brown slurry, dilute into larger buckets, pour mixture over woodchip beds, especially in shady/wetter spots that mushrooms like. Mushrooms that grow wild will take without any fussing about. When they do, keep propagating them elsewhere.