He probably got it from one of the Emacs source repositories, like this one: http://savannah.gnu.org/bzr/?group=emacs
As far as the dependencies, you could install the yum-utils package and then run this:
That will show you everything needed to build emacs from source and ask if you want to install those dependencies. Even though it's for the Fedora emacs source package (23.3 as of F16), it should still work for the generic emacs 24.x source. For example, with those dependencies installed I was able to build emacs 24.0.91 like this:
$ bzr branch bzr://bzr.savannah.gnu.org/emacs/trunk
$ cd trunk
It took about 34 minutes to compile, but it worked.