This is the largest 'scholarly' selection that I am aware of that is in alphabetical order by topic (headwords). Sadly, it is not as selective as that by Rhoda Thomas Tripp ("The International Thesaurus of Quotations", ISBN: 0690445857). Rarely does Mencken provide sources for quotations (usually, just the author's name, with no title of the source, let alone page numbers). The absence of an Index of Authors may be pardonable in a tome of 1347 pages. Perhaps we will see a computerized version some day... ( )