The GEF zip file was obtained from:

http://www.eclipse.org/downloads/download.php?file=/tools/gef/downloads/drops/3.7.2/R201201171043//GEF-SDK-3.7.2.zip
http://www.eclipse.org/downloads/download.php?file=/tools/gef/downloads/drops/3.9.1/S201308190730//GEF-SDK-3.9.1RC1.zip

The zip file includes the sources.