I finally found the reference to the guns being found at Magnolia

United States. War Dept.. The War of the Rebellion: A Compilation of the Official Records of the Union And Confederate Armies. Series 1, Volume 48, In Two Parts. Part 2, Page 835, Correspondence, etc., Book, 1896; digital images, (http://texashistory.unt.edu/ark:/67531/metapth139841/ : accessed August 04, 2013), University of North Texas Libraries, The Portal to Texas History, http://texashistory.unt.edu; crediting UNT Libraries Government Documents Department, Denton, Texas.