Some help...

No surprises here . . . All recordings of Hitler's voice are in German. (He spoke no other language.) The bulk of WWW material is in English because made available by English-speaking people. (Hitler material may also be under some sort of government ban in Germany.)

By contrast, you could probably buy vinyl records totalling several hours of Hitler speeches.

www.nizkor.org

has a considerable amount of material dedicated to some of the psuedo-scientific 'evidence' supposedly refuting certain claims: diesel engines couldn't suffocate enough victims, no measurable amounts of toxic gas were in the walls at Auschwitz, etc. And there is a nice section on logical fallacies which come in handy in any disagreement, including revisionism:

This is an odd reaction for (presumably) a student at Cardiff university. Generally, those listening to recordings of Hitler's speeches are bored and amazed at the crudity of his rhetorical technique. They were electrifying to Germans of a Nazi persuasion listening to them live at the time, but that seems to have been the extent of their success. What is it, precisely, which transfixes you?
http://www.nizkor.org/ is a good place to start.