Here's the offical Apple one... http://store.apple.com/us/product/MB571Z/A/mini-displayport-to-dual-link-dvi-adapter
I'm sure there's a cheaper third party option too. Just make sure it specifically says "dual link DVI". From what I've read, mini DP adapters work out of the thunderbolt port, so I think searching mini DP to dual link DVI will give best results.
(edit) Save some money going with monoprice: http://www.monoprice.com/products/product.asp?c_id=104&cp_id=10428&cs_id=1042802&p_id=6904&seq=1&format=2