You've got a few options.
I'm pretty sure there are online chapters of Beta Sigma Phi, so you could look into that.
Many, but not all, NPC sororities offer alumna initiation. AI is a long and difficult process, and not to be undertaken lightly.
Also, some non-NPC sororities (including the NPHC sororities) have citywide chapters. If there's a citywide chapter where you are and you think it's a good fit for you, you could approach them.
You also have the option of starting a local sorority with some of your friends (if greek life is not outright banned at your school). This is also a long and difficult process.
Good luck.
