Look in the files etc/DISTRIB and etc/FTP for information on nearby archive sites. If you don't already have GNU Emacs, see section What informational files are available for GNU Emacs? for how to get these two files.
The latest version is always available via anonymous FTP at MIT:
/prep.ai.mit.edu:pub/gnu/emacs-18.58.tar.Z
See section Where can I get other up-to-date GNU stuff?.