Instructions
Exchange friend codes with a "Pokemon Diamond" player. Add the friend code of the player to your Pal Pad. Have the player add your friend code to his Pal Pad. If you don't have a friend code, set up your Nintendo Wi-Fi Connection to get one.
Request that the "Pokemon Diamond" player catch Larvitar on Route 207. On this route, all Larvitar will be Level 7. The player will need to use the PokeRadar, a gift from Professor Oak, to encounter a Larvitar.
Catch a Pokemon to trade for the Larvitar. Ask the "Pokemon Diamond" player for suggestions. Since Larvitar is a Pokemon exclusive to "Pokemon Diamond," you may wish to obtain a Pokemon that is exclusive to "Pokemon Pearl," such as Slowpoke, Pinsir or Glameow.
Meet the "Pokemon Diamond" player in the Pokemon Wi-Fi Club, which is accessible from any Pokemon Center. Invite the player to trade by highlighting and selecting "Invite" and "Trade."
Offer the Pokemon you caught for the Larvitar. Wait for your friend to select the Larvitar to trade. Confirm the trade. You can talk to the player via Voice Chat during the trade. The Larvitar will be in your party after the trade. Leave the Pokemon Wi-Fi Club.
Give 23 rare candies to the Level 7 Larvitar to make it evolve into Pupitar at Level 30. Get the Pupitar to Level 55 with 15 rare candies. At Level 55, the Pupitar will evolve into Tyranitar. You can get rare candies by using the Dowsing Machine around Sinnoh or by keeping a Pokemon with the Pickup ability in your party.