The source code is available in a Git repository: eide/emacs-ide.git.
You can get a local copy:
git clone git://git.tuxfamily.org/gitroot/eide/emacs-ide.git
The master branch requires Emacs 24. For older versions of Emacs, you should use the 1.12.x branch. Some bug fixes and enhancements are backported, but there won’t be any official release on this branch.
The source code of the 1.12.x branch is available here: eide/emacs-ide.git (1.12.x branch).