*thinking...what would people do if the net were not available? thinking...why don't you act like the net is NOT available...
An excellent point. I rushed in 1990, when the Internet didn't really exist in the capacity that it is now. (sure the Arpa-Net has been around since the 1940's, but that's another story for another day).
Anyhow, what I did back in the pre-WWW era was get this Directory of Organizations (it had mailing addresses in it) and just write a general (hard copy) letter to the HQ's and telling them that I was contemplating NPC rush and asking for a general, "public relations" type of pamphlet so that I could learn about their organization. Most wrote back and provided me with a pamphlet and a nice "Glad to hear that you are interested in sororities" letter.
Since back then, I was relatively "green" to the whole sororities idea, I got confused between ZTA and Zeta Phi Beta and wrote to Zeta Phi Beta, but nonetheless Zeta Phi Beta sent me a nice general PR pamphlet, which was interesting to read and which to this day, I have kept!
Mind you, that was for NPC groups and I live in Canada, so Greek information is pretty scarce. Thankfully, the Internet is here for you and there are tons of HQ websites to explore and learn from!