It would only be a matter of time before you'd see the GeForce GTX Titan Z  listed 'somewhere', and hey now it just did. There are two listings. One is sold on Amazon is Zotac GeForce GTX Titan Z and the card is priced at $ 3,999. Then another seller on Ebay has also listed the product at a price of $3,799. 

That card would be the EVGA GeForce GTX Titan Z.  An interesting fact however is that the one on Ebay is listed as pre-order with delivery is estimated between Wednesday July 9th and Tuesday July 15th. 

Built around two Kepler GPUs and 12GB of dedicated frame buffer memory, TITAN Z is engineered for next-generation 5K and multi-monitor gaming. With two GK110 chips, TITAN Z is powered by a total of 5,760 processing cores, or 2,880 cores per GPU.