The Japan Coast Guard has been flying a Gulfstream:
Sailors looking out windows trump technology in jetliner search | Malaysia | The Malay Mail Online
But the press release says civilian.
From a year ago:
Second chance at life comes at a cost - ABC News (Australian Broadcasting Corporation)
"Along with the Orion, the Australian Maritime Safety Authority had at various stages of the rescue mission five planes in the air. Two of those were chartered commercial jets - a Bombardier global express and a Gulfstream 550."