If you don't receive your W2 online, the company will send them to you in the mail. I think you should have already received them though, so I would talk with your manager and let him/her know you don't have them yet.
Contact the HR department. They should be able to help you.
I was a former employee of 7 Eleven, and the best thing really is to speak with your manager. The HR department will probably really hard to get hold of if you're just a store employee (trust me, I've tried!).
If you're registered to received your W2 online, then that's how it comes most times. If you're not registered, then they mail it to the store.
If nothing happens for quite some time, then you may want to contact their Cynthia Noren. She was the VP of Human Resources when I was at 7-Eleven and her LinkedIn profile shows that she's still working there: https://www.linkedin.com/pub/cynthia-noren/11/b08/484
You can contact her on there, or you may also want to simply put some pressure on 7-Eleven's management by posting something on social media about it.
If you're going to go down that route - then I'd suggest sending a message to their Twitter account: https://twitter.com/7eleven
Even though the guys who run the Twitter account won't handle W2s, they'll flag it to someone who does because they won't want stuff like that tarnishing the brands name on Twitter.