A number of reference books on holidays can be found around the call numbers GT 3925-4803, including:
Chase’s calendar of events is another standard (and very thorough) title, with official and unofficial holidays - REF. D11.5 .C482
Reference books on holidays can be in the CE call numbers (calendars). Some examples:
Reference books on holidays can also be in the B call numbers, for those focusing on religion or social etiquette:
Encyclopedia of Global Religion - Basic information about religious holidays and festivals around the world.
Information Please Almanac - Fast facts on, and current dates of, major holidays.
St. James Encyclopedia of Popular Culture, 2nd ed. - Information about American holidays and cultural traditions surrounding them.