First, choose a smaller school. Don't even think about going to a larger school and going Greek. At those places you have to be a freshman to rush and good luck if you're a sophomore. Juniors going through recruitment are just not found anywhere there.
It is not too late to go Greek!
What school are you considering, if I may ask? (Hee hee! AOII might be there!)
I know with AOII, we function well in small schools (big schools too, though) and you can have a GREAT Greek experience at a smaller school too! AND it'll probably be cheaper since a group might not have a chapter house (I know my chapter doesn't).