Gary;

I'd like to know this too. I checked at target and walmart with no luck. I'm sure it can be bought as lab grade sodium carbonate at analytical scientific, but it's probably expensive. For normal buffering, if you don't need to correct for an existing low ph, plain baking soda works fine as a buffer, as the sodium bicarbonate disassociates into carbonate ions in salt water. But it won't raise your ph in the way that sodium carbonate will; for most situations, I would think this is actually preferable.