493 Pokemon total Kanto:151 Pokemon Johto: 100 Pokemon Hoen: 135 Pokemon Sinnoh:107 Pokemon
In HeartGold and SoulSilver only Johto and Kanto are accessible. You will need to play other Pokemon games to see the other regions.
You cant.
You can only go to the Sinnoh region in the games Diamond, Pearl, and Platinum.
compllete your nat dex