I already have 1 Eevee, so how do I get more in Pokemon HeartGold because I want the other evolutions of Eevee.
Well... you can breed your current one with Ditto, or buy another from the Celadon City Game Center in Kanto (after E4), for 6666 Coins.
The easiest way to get Ditto is from Route 47 (41 % chance).