Where to get information on FAA AIXM 5.0 versions of Special Activity Airpace (SAA) files?
One possibility is to contact the FAA National Flight Data Center (NFDC). They provide information as part of the US Aeronautical Information Services (AIS).

NFDC Support Desk email is available on this login page, below the login data boxes.

See also this question: Where to find a waypoints/fixed points, navaids, airports database for other aeronautical data sets in case you need them too.