Instructions
Travel to Goldenrod City.
Enter the Global Trade Station Located in the northwest part of Goldenrod City.
Speak to the receptionist on the far left.
Enter the Trading Room.
Choose "deposit Pokemon." Choose something near to the same level of value as what you will be requesting.
Make a request for Torterra. You will now begin the option to choose the details of your request.
Leave the Global Trading Center. You should continue the game. You will receive a message during gameplay that someone has agreed to a trade.
Return to the Global Trading Center in Goldenrod City to pick up your Torterra.