There are a couple of conversions of the Beech King Air. The Beech 1300 is a 13-seat version of the King Air 200, and the USAF uses a 15-seat King Air 350 (C-12S). Both basic airframes are still produced by Raytheon; I don't know who holds the STCs but Raytheon should know. Used B-1300s would be available.