Hurm you could try subwassertang attached to rocks. For moss that you could attach for rock look at some pictures of
Spiky moss
Christmas moss
Weeping/willow moss
Flame moss (but this grow up more then spreading out)
Java moss is quite common but it just goes pretty much everywhere.
All of these grow slowish, but are relatively hardy.
But I'm practically a beginner at this so someone might have a better answer. Though I think those would be a good start.
Also you could check out dwarf baby tears and dwarf hair grass, tho they are known to be demanding.
Spiky moss
Christmas moss
Weeping/willow moss
Flame moss (but this grow up more then spreading out)
Java moss is quite common but it just goes pretty much everywhere.
All of these grow slowish, but are relatively hardy.
But I'm practically a beginner at this so someone might have a better answer. Though I think those would be a good start.
Also you could check out dwarf baby tears and dwarf hair grass, tho they are known to be demanding.