Apple Cinema Display 24.5 inch to new December 2012 iMacs

Hi there. I have a 24.5" Cinema Display and I want to buy the new iMac that is coming out. Since the display already has a male mini display port I would need an adapter that would let me plug the Mini DisplayPort into the thunderbolt. I've liked everywhere and I can't seem to find any. Can you please tell me where to find them and which one is the cheapest thanks.