I believe that Accurate Armour, located in Scotland, offers a decal sheet. This is from their 1/35th scale waterline model of the Type VIIC, but the difference in scale is not really noticeable.
Alternatively, you could make your own. All you need is an ink jet printer (and PC, of course!) and some of the Testors clear decal sheet and their spray can of clear 'fixer'. The graphic of the Laughing Sawfish, in various colors, is readily available in a number of places on the 'net.f