Camy &c.

Your first choice is:

Fatout, Paul, Mark Twain Speaking. Iowa City: University of Iowa Press,
1976.

This will be reprinted at year end; this is the single most comprehensive
(but not completely so) compilation of MT's lectures.  Fatuout's
Introduction is not to be missed!  I would think tracing those actors &
performers who played MT in the first decades after his death might uncover
some audio files of persons who actually heard MT speaking.  Delivery is
only partially a function of accent; for SLC timing was everything!

Gordon Snedecor in Portland, Oregon