The following websites all contain wonderful information and imagery related to the history of Mardi Gras. Many of them are repositories for one-of-a-kind Carnival items and Krewe records. Please check them out in person or on the web!
The Historic New Orleans Collection: http://www.thnoc.org
Tulane University Carnival Collections: http://larc.tulane.edu/exhibits/carnival
New Orleans Public Library: http://nutrias.org/~nopl/carnival/main.htm
University of New Orleans: http://cdm16313.contentdm.oclc.org/cdm/landingpage/collection/p15140coll31
Louisiana State Museum: http://louisianastatemuseum.org
Krewe of Rex: http://www.rexorganization.com
Arthur Hardy's Mardi Gras Guide: http://www.mardigrasguide.com
Crescent City Doubloon Traders (Club which holds meetings and trades doubloons): http://www.ccdtclub.com