I will actually start the thread out now.
Here is a large Alpha Delta Pi unisex formal shirt from 2010, from Wake Forest. It actually belonged to me but I don't really want it anymore:
EDIT: I decided to stop by a thrift store today to see if they actually did have any Greek shirts. I was not sure if that was truly common or not, but I guess it is. I found these two:
Kappa Sigma size L formal shirt from NC State, dated 2000. "Wine 'Em, Dine 'Em, And It's All Downhill From There:"
Kappa Alpha Order 2005 alumni & parents weekend, size Medium. I don't have a clue where this is from, but it has a picture of a guy in KA letters on the back, and says, "Celebrating 25 years of Larry Darnell Foote's Loyal Service:"
I'll trade for any large unisex Panhellenic shirts or cool Greek Week shirts or whatever, or if you belong to one of these orgs and really want the shirt just shoot me an PM and I will send it to you for free.