Wordorigins.org

Dictionary of Americanisms; Mitford M. Mathews, editor; University of Chicago Press; 1951.

This source is a bit dated, but I place it in this category rather than the outdated sources because it is a comprehensive, one-volume examination of American slang, complete with usage citations. Since the Historical Dictionary of American Slang and the Dictionary of American Regional English are both incomplete, this is about your only choice for American slang beginning with M through Z.