The FAA database has:
16 136s (the amphibs) registered…including one to Edwards…and
3 166s (land AC) with two registered to Edwards.

Here’s a link to the database results…you can check on owners and N numbers:
http://registry.faa.gov/aircraftinquiry/acftinqSQL.asp?striptxt=&mfrtxt=piaggio&modeltxt=&cmndfind.x=21&cmndfind.y=9