I don't know that it was ever actually issued as a postcard, but the drawing
you seek does appear on page 17 of Richard's book, ZEICHNER UND
"GEZEICHNETE" (Berlin, 1912). Richards was a German cartoonist who met Twain
in 1907, and the first 11pp. (pp. 9-20) of his book concerns Twain, with
various drawings, photos, and facsimiles. There are usually several copies
listed for sale on the net, usually at modest prices, but not in collectors'
condition, but perfectly fine for research.

Kevin Mac Donnell
Austin TX