Airspace Files (entire US - charting cycle effective September 13, 2018)
These files contain US airspace information for the entire United States, extracted from the FAA's National Airspace Resource data.
You can also get airspace information for smaller regions by requesting a custom airspace companion file as part of an airport information query.
You can follow this link to find files containing US/Canada and US/Mexico border information.
These files also contain information for Class E surface areas, Note however that the Class E sources have been marked by the FAA as "BETA - NOT FOR NAVIGATION)".