The WTP (Web Tools Platform) zip file was obtained from:

http://www.eclipse.org/downloads/download.php?file=/webtools/downloads/drops/R3.3.2/R-3.3.2-20120210195245/wtp-repo-R-3.3.2-20120210195245.zip
http://www.eclipse.org/downloads/download.php?file=/webtools/downloads/drops/R3.5.1/R-3.5.1-20130913223750/wtp4x-repo-R-3.5.1-20130913223750.zip

The zip file includes the sources.