epsom salts can be found in any grocery store and are cal/mag
1 tsp per gallon seems to be the advice I've read on these boards, but be aware feeding cal mag can cause lockout if you're overferting, use it if you need it
or ebay seems to have many suppliers to choose from, good luck man
Sweet thanks for the comment cornflake. I have been using epsom salts and I was under the impression cal/mag was a liquid form. Thanks for clearing it up for me.