I ended up getting 1kg buckets of fine pink salt, epson salt and bicarb soda from these guys
https://www.blants.com.au/natural-epsom-salt-food-grade-0/
then i ordered now foods potasium cloride from iherb.com
https://au.iherb.com/pr/Now-Foods-Potassium-Chloride-Powder-8-oz-227-g/777
no idea what the resulting SJ is supposed to taste like, but it seems consistent with what people say it does. Pretty happy got enough supplies for a very long time