w3m.el is part of emacs-w3m.
To avoid confusion, note that we have:
- [Wikipedia:w3]: aka Emacs/W3, a text-mode web browser completely written in elisp; includes w3.el
- [Wikipedia:w3m]: a standalone text-mode browser much like lynx. Not related to Emacs.
- emacs-w3m: an Emacs interface to the w3m browser. Includes w3m.el, not w3.el
The w3 homepage says "Development has been dormant for a couple of years, so expect bugs due to bit rot."
w3m.el is in the emacs-w3m package, available from the emacs-w3m homepage. This requires w3m to be installed. See the emacs-w3m page for details.