You can find it at Walmart, but it's a seasonal thing. If it's not pickling season (which I'm guessing it's not), you're going to have a hard time finding it.
That's good to know about Vitamin C by the way. Now that I think about it, I guess it does make sense. Vitamin C is synominous with ascorbic acid, right? Adding acid=drop in PH. . .go figure.