Kan, Well....a guy over on the USMF had this DCU up for sale. He wanted $25 shipped in the US for it. I had watched another USAF OSI DCU with more patches sell for close to $90 on Ebay a couple months back. I knew it was a rare DCU due to the fact I have only seen two in my years of collecting.
As far as USAF OSI Special Agents wearing DCU's, I think it may have been an uncommon occurence. I have seen several pictures of them wearing DCU's, but most of the time they are wearing civillian type clothing like you said.
Below is a picture of a USAF OSI DCU at the National Museum of the US Air Force. Pretty interesting.
Caption: DAYTON, Ohio -- An OSI agent wore this desert camouflage uniform shirt in Iraq. The U.S. Air Force name tape indicates that the wearer was a military agent. To keep military authority separate from investigative functions, no rank is worn on agents' uniforms. This uniform is on display in the Cold War Gallery at the National Museum of the U.S. Air Force. (U.S. Air Force photo)
_________________ Always looking for Central American militaria 1965 to 1991. Especially items relating to Coronel Velasquez El Salvador Armed Forces