Source code can be found here:
  http://mp3splt.sourceforge.net/mp3splt_page/windows_build.php
as links to here:
  http://prdownloads.sourceforge.net/mp3splt/gstreamer-1.1.14_build_system-win32.zip
  http://prdownloads.sourceforge.net/mp3splt/GTK+3.6.4_build_system-win32-v4-Alex.zip
and here for mp3splt-gtk:
  http://mp3splt.sourceforge.net/mp3splt_page/downloads.php

See licenses in the mp3splt-gtk_libs_licenses directory.