How do I find out my son's APO mailing address in Iraq?

He was deployed May 22 and doesn't have the addy himself yet, but he's the camp nearest Sadr City and I'd like to be able to send him/his unit care packages as they are in desperate need of certain items, being located at a very small, primitive camp with virtually no services (what he describes they do for sanitation of bathroom facilities would horrify you if you hadn't been over there).