Sonar is correct. I manged to collect some shaggy spores - not easy, and after 6 isolations, got a pure product. I had to "race" the mycelium, that is, place some spores on a dish, and cover the spores with another wafer of agar. This constrains the mycelium from growing up and keeps weed mycelium from forming spores which would ruin the plate. when one sees what looks like a pure thread of mycelium, it can be sliced out and laid on another dish. Keep doing this until you get something pure and then let it grow out normaly.
However, I have heard that it is possible to actually bring mushrooms back from the dead. It is said that powdered dry mushrooms when sprinkled on agar can come back to life. I've never seen it, Ive never done it and it may just be bullshit - or it may be that they need to be flash dried but it is worth a try.