Lambda 10 Project at
http://www.lambda10.org/ has complete resources on gay and lesbian issues in Greek life. Also, consider reading Out of Fraternity Row or Brotherhood: Gay Life in College Fraternities by Shane Windmeyer.
You may be surprised how open some of the traditional fraternities are to having gay members. Is there something specific that leads you to believe they wouldn't be? Also, there are several gay fraternities.