which sororities tend to do spring rush?

No one will know until spring. Who gets to COB in spring is determined by spring total, which is not calculated until a week after school starts. Total is median chapter size at that time. This number is affected by how many people graduated in December or may have left their chapters over the course of the fall semester (resigned, withdrawn from school, transferred, etc). Anyone who is below total is allowed to COB until they reach total. When we had 13 chapters, that usually meant six of them could COB any given semester. Whether they actually COB or not, however, is up to the chapter. If the chapter is only a couple off from total, they may opt not to put forth the effort, or they may not publicize that they are going to do COB, instead offering bids to friends of people in the chapter already.

So the short answer is that we won't know for sure until spring. A lot can happen between now and then to affect chapter sizes.

As far as the rec is concerned, it is true some groups will require one before they can give you a bid. My advice is to have people ready to write you one and then let them know you'll need it as soon as you find out who is doing COB in the spring.