Hey Danny,
if a drain cleaner contains sulfuric acid,it will be listed on the label,however almost all of them contain "buffers".Jim is right though Rooto is the one steve recommended and Ive been using it for a couple of years with no problem,Ace hardware usually carries it,if not Im sure they can order it.Its about $15 1/2 gallon.However if you want to save some money and you dont mind a little extra work,some auto parts stores(not autozone or advanced auto)carry battery acid 30%-32% thats just watered down sulfuric.If you boil it down about 1/3rd then you'd be around the 90% mark.And its ALOT cheaper.But remember it takes a lot of time and you'll end up spending out for the heat to boil it down,thats why I just buy the rooto.
Johnny