Dealers order what sells and based on the members here, most Muranos aren't sold with the Navigation option. I ordered mine without ever seeing one in a Murano, but I had seen the system in an Infiniti I35 (although it was the CD based version).
You can always go to Nissan's web site and search for Muranos in stock at dealers within x mileage radius of your zipcode. I'm sure you'll find one or two somewhere.