It isn't a moss, but have you tried Selaginella kraussiana? It will grow as a low mat on the soil and will keep going as long as it gets a dilute dose of fertilizer now and then. S. apoda is similar but perhaps a little lower growing.

I have been experimenting with mosses from around my yard and stuff in terraria as well as outside and I would reccomend you try anything growing in your lawn, and if that doesn't work try finding a really really small vining moss. These are so small they look almost like algae but in fact are small moss plants. Lawn mosses do well in the hot humid conditions of a lawn and the second mentioned I beleive grows on at least 6 continents and can grow tropical. You can also go to the local nursery and scout out all the tropical orchid pots and find pieces of bark that have moss that was grown in the greenhouse they grew the orchid in. I have some kyoto moss I found that way. It would also help to know where you live.