If you can't find a chemical supplier try a pool supply place. Pool supply places usually carry it, not where I live so I go to a raw chemical place, "Colorox" was buying a truckload of the same stuff I get when I was at my place the last time(Thet just water it down). Also if you cannot find it in small quantities, just buy the El Cheapo "bleach" at sams or costco, usually a little stronger than " Mountain Fresh" Clorox or other major national brands.
I had a 6 gallon jug of 12% go bad on me So I think I am going back to El Cheapo "bleach"