So that was a totally off-the-cuff experiment based on some light reading, and while I was waiting for other supplies to arrive. Basically I found some bulk mushrooms at the store which still have mycelium on the stems. I boiled some cut-up pieces of cardboard, mixed in the chopped stems with it, and put everything in a small plastic container where I had drilled a few air holes in the sides. A few days later I discovered buttons prefer manure to grow on but I kept it going anyway, and the mycelium actually grew!
So after about three weeks of growth I had received my oyster spawn and purchased rye and popcorn. These were boiled for 15-20 minutes, allowed to dry for a couple hours, then moved to quart jars and put in the pressure canner for 90 minutes. The next day I built a still air box and transferred the oyster spawn to several jars, and a couple days later I used the same process to transfer the button mushroom spawn to the remaining jars.
Well the oyster spawn did great, but apparently I made a big mistake somewhere with the button mushrooms because I have blue-green mold growing in both jars within a week.
If I decide to try growing the buttons again then my plan is put the stems directly into the grain jars so I can eliminate one step of transferring and reduce the risk of contamination. I’m thinking about using this method for the oysters as well. I’ve never done spore prints and don’t know anything about making agar, but starting off from pieces of stems sure seemed to work with the buttons.