Where I got Zero Mission (Though apparently none of the other downloads here work):


http://www.detonapoint.hpg.ig.com.br/romgba2.html

or, Google's cache'd version is at

http://64.233.167.104/search?q=cache:F4B_jlNu508J:www.detonapoint.hpg.ig.com.br/romgba2.html+metroid+%22zero+mission%22+rom+download&hl=en&ct=clnk&cd=35&gl=us



Where I got Metroid II, and a good source for GB and NES roms:

http://www.picofactory.com/download/rom/consoles/gameboy/games/metroid_ii_return_of_samus