Here's an idea similar to the "immersion method" of learning languages. Before going through recruitment, deliberately put yourself in several social situations where you will have many people around you. If you want, the first time you don't have to talk or interact much. Just being there will help you get used to being around others. Then the next few times gradually increase your level of talking/being with the others around you. You can go to concerts, museums, restaurants, anywhere there will be a large amount of people. A new church is a good place because everyone there will want to greet and meet you, like in recruitment.
Sororities have many introverted members. Keep in mind that not everyone is an extrovert. You'll do just fine, especially if you consciously try to overcome your shyness instead of just trying to deal with it. Good luck.
