To answer your first 2 questions:
1)Yes sororities do have publications we receive and read on a regular basis, but generally they are to keep members up to date with sorority business.
2) If you mean the mailing address of each sorority's national/international headquarters, I'm sure that information can be found on the respective organization's web site (you can find organizational pages at
www.npcwomen.org and
www.nphc.org and in the signatures of most of the girls that post here). If you mean names & addresses of individual members, I seriously doubt the national bodies will release/sell that information. Especially not for solictation/marketing purposes.
I have a question for you. Why just market to sorority women? We're not the only ones who wear bathing suits.
Maybe what you could do, since your first print numbers are smal (there are easily 40,000 women in one sorority), is do a test run on women in your area and see what they have to say, then expand regionally & then nationally. After all, you're running against Victoria's Secret, Vogue, Elle and other major fashion magazines & retail stores that already publish the latest styles.
I know I probably sound like a real downer, but those were the first thoughts that came to my head. I do wish you all the best though.