Working papers are usually available online as part of a working paper series. They allow for the quick dissemination of research findings in the social sciences. They are often pre-publication versions of what will later become academic journal articles.
Working papers are usually published by Universities, research institutes and other organizations. This page lists a number of working paper series including the collection published at University of St Andrews. If there is a particular organization you are aware of which is working in a research area which is of interest to you then try searching in the publications section of their website to see if the working papers are available