for Clausewitz in
archives containing works by numerous key Marxist writers. (This Google engine returned 380 hits from the Marxists.org archive on 3 July 2012.)
* The Library of Congress On-Line Catalog Search System
(an excellent place to find old, obscure, and non-English-language works by or about Clausewitz). A "Basic Search" by keyword appears to be the best way to find interesting items.
*Oxford Bibliographies (editor-in-chief Dennis Showalter) offer exclusive, authoritative research guides. Combining the best features of an annotated bibliography and a high-level encyclopedia, this cutting-edge resource guides researchers to the best available scholarship across a wide variety of subjects.
The Oxford bibliography on Carl von Clausewitz offers information under several headings.