you can get it at bunnings for 6 or 7 bucks for enough to last a decade or so... it's called ph down, used for hydroponics..
the acid is strong enough that it has burned a hole in my kitchen's postform... I don't think any form of life will survive a dunking in the stuff... a drop or 2 per litre will drop ph down a long way (like ph 8 to 6).. from my estimations... there may be other considerations regarding suitability for food use, but others have used the stuff for beer, if that's any comfort...
cheers, Organo