HGSS: Pokewalker question

I read somewhere that when you buy the original game, you get a pokewalker that can get you some new pokemons and items. My questions are:

1.Is it the only way to get some pokemons in game?
2.Can you buy it separately or you need to buy the game to get one?

EDIT: Lolwarning. The beginning of the post was deleted.