Oskosh Panhellenic
UW-Oshkosh has the following NPC sororities:
They also have Gamma Alpha Omega, which apparently is petitioning to be on Panhellenic there. I was a Gamma Phi at UW-Platteville and I know that their system is different because they have Panhell, but I haven't heard anything about their rush being horribly competitive. I doubt being a sophomore would hurt at all, but you are also a "non-traditonal" student because of your age, which may make a difference. I would try emailing the Panhellenic rush chair (contact info on the website) to see what she has to say.
UWO has a pretty good Greek system, from what I've heard - I know our chapter there is strong and I have met some Phi Mus and ZTAs from there who were also awesome!
Good luck!