There is no big index to cartoons, so finding them is a matter of persistence and serendipity:
Frank Leslie's Illustrated Newspaper (also called Leslie's Weekly)
Life Magazine (1883-1936) http://catalog.hathitrust.org/Record/008891350
Phunny Phellow (1859-1872) American Antiquarian Society (AAS) Historical Periodicals Collection
Frank Leslie's Budget of Fun (1866-1876) American Antiquarian Society (AAS) Historical Periodicals Collection
Puck (San Francisco) (1877-1918) American Periodicals
Duke University. Emergence of Advertising in America, 1850-1920
American Memory. An American Time Capsule: Three Centuries of Broadsides and Other Printed Ephemera