Check out this excellent article on a failed project by Thomas Nast for a Th. Nast's Grand Caricaturama:
A Caricamural View of the American Civil War.
The Daily Heller blog (March 7)
In the article, Heller notes, "In 1950 five of the large (8' x 12') paintings were found in a barn in Morristown, New Jersey, where Nast had lived. They were acquired by Erwin Swann, founder of the Swann Foundation of Caricature and Cartoon dedicated to scholarship on comics and cartoons in all media."
DC-area cartoon types should recognize the name Swann - his collection is in the Library of Congress. Swann curator Martha Kennedy confirmed for me that the paintings are in the Library, albeit in off-site storage because they're so large. This search should pull up the catalogue records and hi-res scans of the five 8 x 11 1/2 feet images. Martha also says that 2 more of the paintings survive in the northeast.