Many books on Allied special operations in the Adriatic mention the RSR in passing, but none that I have read mention it in detail, nor have I read any book specifically on it (which is not to say that none exists; I just don't know of any). It is actually a very interesting "lost" unit of World War II.
For some of those brief references I mentioned, the following probably have some:
Strutton, Bill. Island of Terrible Friends. New York: W. W. Norton, 1961.
Stokoe, E. G. Lower the Ramps: Experiences with the 43rd Royal Marine Commando in Yugoslavia. Bath: Chivers, 1988.
Neill, Roy S. Once Only. London: Jonathan Cape, 1947. (my memory on this one could be wrong and it could be some other theater)
McConville, Michael. A Small War in the Balkans: British Military Involvement in Wartime Yugoslavia, 1941-1945. London: Macmillan, 1986.
Jenkins, W. G. Commando Subaltern at War: Royal Marine Operations in Yugoslavia and Italy, 1944-1945. London: Greenhill Books, 1996.
Churchill, Thomas. Commando Crusade. London: William Kimber, 1987.