help

As a junior, you'll have a very hard chance getting into most of the good houses, and not knowing people won't help. Plus, you would be a Junior in a mostly Freshman pledge class, would you really want that? Just saying, but as a junior, a sorority might not be the best option just because it's a lot harder the older you get.

If you don't know any of the girls, why do you have a preference for those groups? National reputation? Legacy status? Philanthropy? Colors and symbol? Perceived tier? Some of those reasons have value, others don't. It is difficult (but not impossible) for a junior to get a bid, but not being open to all groups will bump that possibility into the impossible range. You will need to be open/grateful for any invitations and dance with the ones who invite you.