I'm not sure how much luck you'd have finding a nun's costume for free. That's a pretty specialized need. Have you looked in Renderosity Free Stuff? Look at the link at the top of the page. Be sure to select Poser to narrow down your search. It might be easier if you told us where you've looked already. You could also look in the Renderosity MarketPlace. Some stuff here is actually quite inexpensive. I don't think I've seen a nun's costume at DAZ3D. I think Poserworld had one, or maybe PoserStyle. They're subscription sites.