I just received the following information from NBC.
NBC is holding an auction right now for props from The Office, Heroes, Friday Night Lights & some other shows. It's running through December 3rd, and a portion of the proceeds go to the United Way. They'll be launching more items after the 3rd. These are all actual props - even the "Fun Run" shirt was worn during the premiere episode.
NBC Main Auction Page
For those of us DYING for anything new pertaining to The Office:
Michael's Haiwaian Style Convention Shirt
Roy's Dunder Mifflin Warehouse Shirt
Dunder Mifflen Polo Convention Shirt
"Fun Run" Shirt