Where can I buy carbonic acid in Sydney

I need it to conduct a science experiment for my school SRP, to model and calculate the effect and rate of ocean acidification on calcium carbonate based organic material i.e. coral, mussel shells... etc.

I promise I'm not trying to like... kill anyone or anything. :D

I doubt that anyone sells it anywhere as carbonic acid. It is a very weak acid that forms when CO2 is dissolved in water. Go buy a bottle of club soda ( do they call it that down under?) and you will have a bottle of carbonic acid.

Try purchasing some soda water like when they add soda to whiskey. It is just CO2 in water. Alternatively make your own by placing some dry ice in water and let it stand until all the CO2 has evaporated.