Does it use a radius-based search? When I input a U.S. zip code, I get no results.
The standard Store locator add-on doesn't do search by a zip code. It searches for the store location by a city or country.
I think you may be interested in this Store locator modification New store locator for CS-Cart It doesn't do search by a zip code but does a radius-based search by address/city/country and has some useful features.
Best regards, Alt-team