Finally found the update site for the required version.
update site : http://repository.sonatype.org/content/repositories/forge-sites/m2e/0.12.1/S/0.12.1.20110112-1712/
Answer Source : http://comments.gmane.org/gmane.comp.ide.eclipse.plugins.m2eclipse.user/7972
The update site were not working with 'https' instead given 'http' and worked for me.