The postwar Joint Army-Navy Assessment Committee (JANAC) report. I believe that this copy is complete.
http://www.ibiblio.org/hyperwar/Japa...ses/index.html
Though the sinkings listed are credited to ship each ship, not to the ships commander. If you really need the commander totals, you'd have to cross reference with another data source to get who commanded what and when.
The 25 best commanders are listed here with both wartime claims and JANAC totals.
http://www.valoratsea.com/skippers.htm