Where can I locate a source that provides access to film clips
relating to public speakers for a presentation I am preparing.  I
would like them to be humorous with recognizable actors in
recognizable films.

If you can't find recognizable actors in recognizable films, I highly
recommend the great PRELINGER ARCHIVES.  Legendary source for old
Black & White training films and sales films and other footage from
the 1940's and up -- footage that you can license thru Getty Archives.

But Prelinger ALSO offers some of the archive as PUBLIC DOMAIN (read
their caveats). These short films are are usually very funny, because
they're so earnest and quirty.  You can watch them online and download
them.  If you need to have them in broadcast format, ithe site tells
you what to do.

Simply go to their website and search by KEYWORD.  Typing  "Public
Speaking" on Prelinger turned up several good candidates:

Here's one from 1949:  Stage Fright & What To Do About It
http://www.archive.org/movies/details-db.php?collection=prelinger&collectionid=01173

There's also a 1950 one on Speech and Posture.   And another 1949 one
on Speech and Gestures.

Here's the main URL:  
http://www.archive.org/movies/prelinger.php