I just kept an eye on craigslist for a couple of weeks. I wasn't having much luck until I randomly decided to search "apple monitor" instead of "cinema display". I found someone that was selling an older PowerMac G4 along with an ACD. I just talked her into selling it to me separately.
There's also several eBay sellers that have off-lease ACDs. I don't remember specifically but there was one seller in particular that had some in A+ shape and great reviews on previous ACD sales.
Make sure the cable and power brick are in good shape before you buy. A new one isn't cheap.