try http://www.freeroms.com/, but many links no longer work
I found some stuff on the following sites (most in french, because that's where I surf):
http://www.emulation64.net/ (follow the forums and the links)
http://rpg-legends.com/nintendo_64.php
h
ttp://rom-n64.gratuit-free.com/
http://www.n6
4emu.net/

and, I suppose, about a zillion other sites :)