Scientific American Archive Online on Ebsco
It would seem that the Scientific American Archive Online is now only available on EBSCOhost:
This stand-alone database includes ongoing coverage for the publication in addition to backfile content beginning with the January 1993 issue. The Archive also contains the newly launched publication Scientific American Mind (starting with the premier issue from late 2004), as well as all Scientific American special issues dating back to 1997. In keeping with the archival nature of the database, each of the more than 5,300 articles is made available as a full color PDF, thereby maintaining the integrity of the original printed page – including all of the graphics.
A free trial is available, email for details.