You can get it from coles however one box = one bath, so not very cost effective. I can get a 25kg tub for a good price (once u break it down per kg) but its a lot to order in. Aldi once upon a time had them in the special buy really cheaply as well.
Where do you get the 25kg tub from, and how much is it? I got 2kg for $13,95, which was the same price as I was charged for 500g in the pharmacy (criminal I swear!). I am trying to use 1 cup (250g) per bath, so even 2kg is only 8 baths worth, so I think I will need to buy in even bigger bulk.