This page from the National Archives website may be helpful: http://www.archives.gov/veterans/military-service-records/replacement-medals.html
As to obtaining an Armed Guard patch or flag, I suggest that you contact Mr. C.A. Lloyd, Chairman, U.S.N. Armed Guard World War II Veterans Association, 115 Wall Creek Drive, Rolesville, NC 27571; telephone: 919-570-0909; e-mail: email@example.com
Your father may be interested in joining the Armed Guard Veterans Association. Mr. Lloyd will have information.
Ron Carlson, Webmaster
Armed Guard website