You can order the update online from Nissan (special pricing through June 30, 2013), which comes with 5 DVDs. Apparently, you have to provide the Unit ID for your navigation system in order to get an activation code. I looked around for a torrent, but only found an old 2009 version with no explanation regarding the activation. I'm guessing it will be extremely unlikely that someone bothers to crack the activation.
Nissan Nav Map Update