I bought mine from CR's Crafts online, where you need to search for "9mm eyes" in order to find them. I got a package of 50, so I now have what amounts to a lifetime supply. I realize that ordering eyes online (and paying shipping) may not be convenient or even worth doing for many people, but I wanted to provide the link for those who were interested. I'm sure that other online craft suppliers probably have the same eyes available.
Of course, you could always do embroidered eyes or button eyes instead. Or try Knitflix's solution and sew on felt eyes. She has information about this technique on her blog.