There are a number of multi-collegiate, multicultural sororities. The "multi-collegiate" part may not mean that many colleges, but there are others out there.
I would suggest a search of the internet, a thorough perusing of this board, and actually talking to members of several different sororities - NPC, NPHC, local and other - to get to the real reasons women join and stay in sororities.
You could start here:
http://nationalmgc.org/
This organization doesn't cover all the various such groups, but it's a start.