Results of an AltaVista search: "koreans in japan":<p>
<a href="http://www.han.org/ ">www.han.org/</a>  ("HAN is a project provided to promote a better understanding of
Koreans in Japan from two different viewpoints, scientific and cultural.")
<p>
<a href="http://www.skas.org/">www.skas.org</a> ("Society of Korean-American Scholars (SKAS) is a private, nonprofit and nonpartisan organization dedicated to engender
 intellectual exchanges in the global Korean community with a view to enlightening and empowering individual members of
  the community. It promotes scholarship and fellowship among its members and seeks to foster leadership among young
                                        Korean-Americans.")
<p>
<a href="http://www.columbia.edu/cu/cup/catalog/data/071030/0710306237.HTM">Lives of Young Koreans in Japan</a>
Yasunori Fukuoka (a book to get by ILL)
<p>
<a href="HTTP://pslab11.polsci.wvu.edu/Grad/dkim/ps355res.html">The Longitudinal Study of Agenda Setting Process in Japanese Ethnic Korean Policy</a>  
(David K.S. Kim)
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<a href="http://www.knj.com/">KNJ Network Service</a> ("provides information on Koreans in Japan and other countries")
<p><a href="http://www.feedmag.com/html/feedline/98.01gaiter/98.01gaiter1.1.html">Koreans in Japan</a>: Past and Present
                                    (FUKUOKA, Yasunori 

                                Saitama University Review, Vol.31, No.1.)
<p>
<a href="http://www.kimsoft.com/korea.htm">Korea Web Weekly</a>
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<a href="http://yuldo.net/">uldo.net: A Korean Studies Site</a>
<p>
<a href="http://www.korealink.com/">www.korealink.com</a>
<p>
<a href="http://www.knj.co.jp/korean/KoreansJP.html">some data by Prefecture</a>