Do sorority members host events or fundraisers on campus that you could attend? Are they visible on campus? Are there opportunities to strike up a conversation with them?
For example, my sorority hosted a pageant every year as a fundraiser that was open to the entire school. We also posted tables around campus during finals week and gave out candy - Smarties and Dum Dums. Adorable, I know
These types of scenarios can present a chance to talk to them or ask questions.
Also, don't feel completely rejected. Even if conversations didn't click during round 1 and you were cut by most of the chapters, they're basing decisions on one conversation. It's certainly not a perfect system, and some potential members don't "shine" in such a setting, as someone else said here. Informal might be your best option. Or try formal recruitment again and practice conversations ahead of time. Were you giving a lot of one word answers? Try thinking of the questions you were asked and prep some complete, well-thought-out answers. For example, if someone asks you what your major is, don't simply say, "Biology," and move on. Explain why you're interested in the subject and what you hope to do after school.
Regardless, if you feel this is something you truly want, don't shrug your shoulders and give up. Try again and make sure you have your ducks in a row. Good luck!