Cheap and easy source of good fine moss. "Crack in the Sidewalk Moss". I know you are in a dry climate, but look for an area where there is a sidewalk that is always shaded, say north walk along a tall building. Glance down at the expansion joints, & the cracks. If there is an often watered patch of lawn near by, you might get lucky and find some. Here in the midwest it is everywhere. This is the most commonly used moss by bonsai people in the US. It becomes a thin mat once established in a pot. Tear up the harvested moss into little pieces, scatter over the surface you want to propagate it on, then cover with a thin layer of the same media, then water.
I keep a seedling flat growing nothing but 'sidewalk moss', it is planted with the fines from my bonsai soil. The entire flat becomes covered with moss, I am able to harvest part or all about every 2 months. If you take off a thin layer, the layer beneath does not have to be re-seeded, or re-colonized from the other side of the flat, the 'roots' (not botanically correct term for mosses) will form a new mat, the green visible in a week or less.
Just a thought.
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