Stan,I can totally identify with your situation. When I first pledged at Ball State in the late 80s,my chapter had 13 brothers and 13 pledges. We decided we wanted to change things around, and we won Greek Week that year (back when Greek Weeks were still competitive) part of our prize was a free skating party with the winning sorority, who happened to be Chi Omega, and who were easily the most sought after sorority back then. A free skating party, and basically they had an excuse every time we tried to schedule it with them. For two years we tried to have this skating party and it never happened. What's truly ironic though, is that most of our alumni from the 1970s all seemed to be married to Chi Omegas! Apparently at one time, we were good enough to marry, but not roller skate with! But that's not helping you with your problem...
If no sorority as SDSU wants to mix with you guys, try inviting a sorority from USD or another school that's nearby. I know this happened a lot with some schools in Indiana. Wabash College is the last all Men's school in the U.S., and has a very big fraternity system. They used to pair with sororities from DePauw, Butler, Purdue, even Ball State (which is quite a ways away).
Also, are there any sororities that aren't considered as "desirable" among the fraternities at SDSU? If there are, these groups will probably be more likely to want to have mixers or do something with your chapter.
Finally, invite individual sorority women that you know and are friends with to come to some of your events. It can take awhile, but this is a good way to build up a following. It worked with my chapter, and eventually several women from the same sorority who had come to our parties and other events, and who knew us to be nice guys asked in their chapter, "Why don't we ever do anything with the Phi Sigs?" and got our foot in the door.
Good luck, I hope this helps.
