I started getting liquid chlorine and muriatic acid from Best Pool Supply (Folsom Blvd, Sacramento).
They have gallons of 12.5% at $3.75 which is about the same as the 6% great value, but if you mention the buy 3 get 1 free deal from their website it is a great deal.
You do have to put a deposit on the bottles and the 4 pack carrier and return them when you are done. I prefer this to throwing a pile of bottles in the recycling.
Gallons of Muriatic Acid are $4.25 for 31.45%...cheaper than you can get in a paint department. Same deal on bottle deposit.