I'm not sure what the legalities of it are over there, but you may be able to find some nice mosses you like the look of in a damp wild place near where you live.
I've heard of people using "Oasis" floral foam to mount orchids and keep them damp.
With time, you don't actually need the moss there for a lot of species - it's mainly there to keep them damp whilst they get used to the idea of being mounted, so you could always pull the sphagnum off (slowly!) over time, once the plant(s) have established.
I'm sure more experienced orchid mounters will weigh in shortly