Library of Congress Subject Headings is an alternative to keyword searching. They can narrow down your search much more effectively than keywords.
Here are some good subject headings to use in your searches on Comparative Politics
Encyclopedia of Political Thought by 
International Encyclopedia of Political Science by 
The Oxford Companion to Politics of the World by 
Encyclopedia of Crime and Justice by 
Encyclopedia of Criminology by 
A New Handbook of Political Science by 
The Oxford Handbook of Political Theory by 
21st Century Political Science by 
The Oxford Handbook of Criminology by The Blackwell Dictionary of Political Science by 
The Facts on File Dictionary of American Politics by 
The Palgrave Macmillan Dictionary of Political Thought by 
The Routledge Dictionary of Politics by 