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.