Check this site The Java programming-language compiler (javac) group. The sources are in the Mercurial repositories.
jdk7/tl/langtools (for JDK 1.7)
jdk6/jdk6/langtools (for JDK 1.6)
In the header of the two sites I linked to you find download links for the sources (in bz2, zip and gz format)
There you have the sources in src\share\classes\com\sun\tools\javac\
