I buy mine from a chemical supply company 2 pounds at a time for about 45 dollars which is enough to make about 30 4 oz bottles. I use to by it on ebay, but last time I checked they didn't have any. Check out Jim humbles site [link to jimhumble.co (secure)]

He is the one who discovered its present day uses accidentally while mining in south america. He was using it for water purification and gave some of the water to people with Malaria and they got well. I'm sure he has some suppliers listed on his web site. It would seem the government is clamping down on its promotion for human use, imagine that. lol