They're quite rare, as far as I know! I have one myself, but... how I got it is probably saved for another day once you're more used to this place.

*He gives a tiny shake of his head in response to that!* It was a tiny out of the way shop in the Goldenrod Underground, called Torkoal's Smokes... So I doubt it's a chain... Still, it should be easy to find if you know the name.