However, you can catch Raikou and Entei in HeartGold, which are the other two legendary beasts. Here's how:
1. Beat the game: You need to complete the main story and become the champion of the Johto region.
2. Find the legendary beasts: After becoming champion, you'll receive a call from the game's protagonist who informs you that Raikou, Entei, and Suicune have appeared.
3. Track them down: The legendary beasts roam the Johto region randomly. You can use the radar to find their locations.
4. Prepare for battle: These Pokémon are very powerful, so be sure to level up your team and prepare for a challenging fight.
5. Catch them: Once you've encountered a legendary beast, you can attempt to catch it using Poké Balls. Be prepared to use multiple balls and possibly Ultra Balls or Master Balls for a better chance of success.
Remember, legendary Pokémon are extremely rare, so you may have to search for them for quite some time. Good luck catching them!