Most people would get this from a Laboratory supply house. Most of these are very reluctant to sell to private individuals since they have more than reasonable right to believe that it will not be disposed of properly and then the supply house is eventually liable. Next is safety, Battery acid is used by lots and lots of non trained people, because it is not instantly serious if you get some on you. Very pure Sulfuric Acid will burn most peoples skin in less than 5 seconds. Case and point, the old lady that spilled a cup of coffee from McDonalds on her privates and burned them.
Battery acid is like a large firecracker as very pure sulfuric acid is to a small stick of dynamite.
Please do not feel picked upon if no one will sell to you. James is correct, It is bad stuff but that just means you have to be REAL carefull. You MUST wear safety glasses and ALSO a face shield when working with this stuff. A source of concentrated sulfuric is liquid drain cleaner sold in hardware stores. Just read the label.