All of the source code is host on sourceforge, you can browse the current tree here:
http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/kmeleon/k-meleon/ or follow the instructions here
http://sourceforge.net/cvs/?group_id=14285 to grab the source via cvs. "K-Meleon" is the directory you want, and the .5 branch is tagged "kmeleon05"
-- Jeff