I just ordered some plugs (to put in logs) from Fungi Perfecti. They have a website that has lots of information to read. They do have materials to put into a garden bed like you're describing, and as I recall, there are lots of varities (including lots I'd never heard of) you can get that way. I'm not sure how it works to have different varities in the same bed. At Fungi Perfecti, they do sell a book (though it's cheaper at Amazon) on growing mushrooms.

I looked into it because although I love gardening, a huge chunk of my acre property is woods. I can't enlarge my veggie garden, and we love mushrooms. So why not grow some? With the woods, the logs are no problem. Actually, the power company just trimmed out front this spring, so I have all kinds of logs to choose from. I'm hoping it works.