"MIRAD" You mean MARAD? The Maritime Administration, the operator of the largest historic ship fleet in the world?
MARAD isn't likely to have weapons mounts as weapons systems continue to be owned by the U.S. Navy. The Navy is unlikely to have any lying around, especially for a system that hasn't been in service since the 1970's. See this site for more details about the Bofors 40mm in U.S. Navy service: http://www.navweaps.com/Weapons/WNUS_4cm-56_mk12.htm
The Naval Historical Center would be a good place to start to see if any mounts are available for loan: http://www.history.navy.mil/