The pure Vitamin C would have to be Sodium Ascpobate, which is the non-acidic type. I bought this for health reasons at a pharmacy, and I know it is used in the culinary industry as well for keeping food fresh when you don't want to use lemon juice (perhaps because of the flavor does not match what you want to use in the dish). When asked what it tastes like, my most common answer is "like salt, but without the salty taste". By this I mean that it simply is not as "salty" tasting. But do be aware: it has sodium as well, so I don't know whether it really reduces the health risks associated with salt.
One thing that I also use for health reasons is Alum powder, which is often used in pickling spice mixes. It tastes salty, sour and even a little sweet, and could probably be used in a mix similar to Mrs Dash. Again, I believe it has some sodium, or else might have sodium, but as I understand it Alum is actually a classification of chemicals rather than a specific one. Anyway, it provides relief for my canker sores