Instructions
Travel to the harbor at Olivine city and speak to Professor Oak, who will give you the National Dex.
Take Route 48 north and then west past the bridge to reach a large grassy area. Head north to the Safari Zone Gate, enter and speak to Baoba. When he questions you, reply yes. Then speak to the man near the top to pay a fee and gain access to the Safari Zone.
Complete the monster hunting challenges given to you by Baoba. Hunt and capture a Geodude in the cliff area. Place it in the first party slot and speak to Baoba. Wait up to a day for his call, during which he explains you have the ability to customize the environment.
Enter the desert area and capture a Sandshrew during the second monster hunting challenge. If you don't have access to the desert yet, use the customization tool to rotate it into your available locations. Place the Sandshrew into the first party slot and speak to Baoba again. Wait for his second call; he explains you can place certain objects in the Safari Zone.
Travel to the Sahara zone and press the "A" button to pull up your inventory. Choose the "Rocky" item. Drop 30 of these anywhere in the area, with the exceptions of water and grass. Hunt for and capture a Skorupi Pokemon. The "Rocky" items cause it to appear, and Skorupi will show up more quickly with 30 items placed correctly, but you will still need to wait a while before it does.
Ascend your Skorupi to level 40, at which time it will evolve into a Drapion.