Ask EVERYONE you know who attended college if they were in a sorority (or know women who were) and can help you out. If you don't succeed there, go to this website, find the group nearest to you, and see if they can help you.
http://www.npcwomen.org/alumnae-panh...directory.aspx
Soliciting rec letters on Greek Chat from posters you don't know from Adam and vice versa is considered inappropriate.