Hello Decent 1,
I don't know how it is in Australia, but here in the UK the only moss you can buy is the sort used to line hanging baskets, it's much to thick and high to use on top of bonsai pot soil.
In the winter and spring the sort that grows thick and flat grows naturally on walls and paths here, but in the beginning of summer I never have enough. This is what I do. Put some potting compost in a tray, about and inch deep. Soak it and place in deep shade, water every day. After 2 weeks you can see moss forming, after 4 weeks is ready to lift with a knife and place on soil of bonsai pots.
