Um, I was just playing my Pokemon SoulSilver version and I found the Safari Zone. After walking around for a few minutes I got bored and headed for the exit and a Pokemon appeared, it was Mr Mime. I came to this site to see how rare it is to find one(since I found one so fast) and saw that your Pokedex does not have information on Mr. Mime being in the Johto Safari Zone. So, I don't know how rare it is or what seasons or hour on finding it or what the level range on them is but you CAN find them in the Safari Zone.