Hmm... in Canada that is one of the basic best selling flavours... you basically have to offer salt and vinegar if you sell chips. Is it really that uncommon in the states. I mean I heard it's hard to get ketchup flavour down there, but I wouldn't have suspected salt and vinegar as being rare.
As an American fan of salt and vinegar chips, you’re never having a hard time finding them, but they’re not in the variety packs and if you bring them to a cookout without any other flavors you will get mean looks. Though really the only flavor other than plain that wouldn’t get you mean looks for only bringing it is barbecue (maybe jalapeño)