Peat Moss should be easy to find. You want pure sphagnum peat. Usually/ possibly always compressed which means even the smallest bag/bale will probably be overkill or enough for a lifetime of Wabi's!
I mix peat and compost 3 to 1 get it pretty wet, then squeeze the water out and it holds it's shape quite well. A layer of moss around the ball (to help hold it together) with plants and additional moss here and there works nicely.
Cool! Thanks for the info. Any particular brand of sphagnum moss?