I have no idea where one goes to buy an Oscar knockoff. My not-so-helpful advice: The dress I wore to fajitas' wedding, which I am delighted to be able to wear a second time (to foldedfish's wedding) is fairly formal. (You saw it, did my hair for it, and took a picture of me in it. :) ) I got it at Filene's Basement. I don't know if this helps at all, or if Chicago has Filene's. Also, it occurred to me as I wandered through David's Bridal this year that I would totally wear some of those bridesmaid's dresses in some of those colors, and those might be Oscary.