That's probably your only option. The only fully downloadable shortwave broadcast schedule I know of is the Eibi one, and while it includes almost everything from broadcast stations to military stations, channel markers, utility stations, and even some regular pirates, the listing of numbers stations is incomplete, and the ones that are listed are usually given different names from the standard ENIGMA designations (e.g. "Cuban Spy Numbers" rather than "HM01"). Maybe someone on their IRC chat knows.