Fantastic that you're planning a bigger one!
In Arizona, we have a low spot in our yard. Our soil is mostly clay, so it holds water a long time. We don't get much rain, but when we do, it stays wet for so long that moss forms on top. Ask around. Maybe some of your friends know where to find it! Some nurseries do carry it or can order it. If you get a little bit, you can grow more easily.
I've read that you can take moss and mix it up with buttermilk and "paint" it on surfaces you would like to have mossy. Apparently the buttermilk makes the moss happy and it grows where you paint it. Here is a link telling more about moss and propagating it.
http://www.wikihow.com/Grow-Mo...
PS, where did the piano go? Will it go in the larger ruins?
