Ace hardware sells 2 kinds of sulfuric acid drain cleaner.
Professional drain cleaner (I think that's the name) in a white 1 gallon bottle.
Liquid Fire drain cleaner in a 1 gallon red bottle, both around $20 US.
Calcium nitrate in a 3Lbs bag, I around $12 US
You might find sulfuric acid at Lowes/Home depot, buy usually I only find their drain cleaner as sodium hydroxide, only good for PH adjustments.
Lowes/Home depot sell Potassium nitrate as Spectracide stump remover (black bottle)...not to mistake it for Bonide stump remover as it is SMB.
Located in Virginia am pretty positive there are farmer stores/markets you can find other nitrates available...If your not a farmer, I wouldn't go a get a 25Lbs bag though...You may get some questions on why you need that much. I would buy a couple Lbs at a time.....for the garden of course.
My wife hates when I standing in the store isle's read ingredients lists looking for chemical substitutes for refining
.