A supplier says he carries 32% hydrochlorous acid? What exactly is this?

I suspect a typo.

I just googled it; wikipedia says it's very unstable, which in real terms means if it's 32% when bottled, it won't be anywhere close to that by the time you get it home.

Hydrochloric acid is common.... also called Muriatic Acid. Typically sold at 31.45% for some reason unknown to me.

I think that the reason is that acid was traditionally produced according to the Baumé scale, and that 20 Baumé is 31.45 %.