You might try contacting Braodfoot Publishing because the casualty list from George Cupples, Chief Surgeon Wharton's Cavalry Corps done on May 26, 1864 at Bayou Des Glaise, Louisiana is printed in their book The Supplement to the Official Records of Union and Confederate Armies, Edited by Janet B. Hewett, Part III-Correspondence, Vol 3, Serial No. 95 (Wilmington, NC: Braodfoot Publishing) 1999. Evidently someone working for Broadfoot encountered Cupples' reports and may be able to direct you to the location of the originals.