I doubt you'll get one at MA, is the CO2 aerosol or fermentation based?
You'll need 4dKH water and an acid based indicator such as Bromothymol blue also.
Look on ebay, there are some kits on there, most come with the indicator, you'll still need the 4DKH water however, though if you have a low range PH test kit, that should be a suitable indicator.