You can only get one Eevee in Crystal version, the one you get from Bill. If you want more, you'll have to breed your Eevee at the daycare center with a pokemon in the same egg group. The easiest way to do this is with a Ditto.
On a side note, Breeding Eevee and hatching one from an egg is a great way to get its happiness up quickly, great if you want an Umbreon or an Espeon.
