I've seen it at the Super Walmart center in Cicero, but I don't recall ever seeing it at the smaller ones.
I actually used to buy the distilled water at Walmart, instead of the ro/di. It was run by Culligan, but I didn't know how often they changed their filters. I think it was 59 cents a gallon for distilled, and they'd come in gallon jugs. 3-pack of gallon jugs @ the Super Center.
I think if you don't bring your own container, it's not worth it over the distilled.