Well if you're looking to start a national organization your options are basically wide open. Since there are no other nationals on your campus you don't have to worry about Panhel approval - just recognition from your school. To learn about nationl sororities a whole definitely browse the
National Panhellenic Conference homepage. The site should have some info about starting a chapter. You should also consider writing to several sororities explaining your situation and expressing your interest in forming a chapter. Part of the reason we affiliated with AEPhi was because of how helpful they were when we were forming. Its a long and hard process (though totally worth it!!!) so you want to make sure you find a national that's going to work with you!
Best of luck!!