The aircraft involved were Fairy Swordfish, the first attack by 825 Squadron from HMS Victorious on 24 May (lead by the legendary Lt Cmdr Eugene Esmonde). The second attack was by acft from Ark Royal on 26 May and it was in this attack that Bismarck's rudder was damaged.
My books are packed away but you say you've read them. A search on Google found these two sites
http://www.kbismarck.com/ and
http://www.bismarck-class.dk/ (and presumably others), neither of which names the pilot. If the name is known then it would be in the reports in the Public Records office at Kew but in which case I am sure it would have made the various books, so perhaps it was never certain who dropped that particular torpedo.
Anyway, thanks for making me find those two sites. Now for some interesting reading!