I would bet there are various bromeliad and orchid vendors in Australia with boatloads of tropical moss they don't like.
Exactly. Just get yourself some greenhouse weeds. Who cares if they're common? They're still mosses, if what you want is "just some nice live green mosses". The fact that they're opportunistic, early-successional species is a good thing for our purposes.
Note, there will likely still be a little variety among greenhouse weed mosses. If you can actually get inside a greenhouse, you will see various taxa:
- on the substrate (probably gravel) under the benches,
- on the benches themselves, especially if they are wooden benches,
- on the soil surface of whatever potted plants are in there, and
- on any wooden stakes or other supports for vines or epiphytes
Grab a little bit of everything, and see which ones like the inside of a vivarium.
Failing this - how about a roadtrip up top?