The remote is often on a velcro mount somewhere around the car. Many owners dont do this though as it advertises the fact that a sat nav is present.
Its about the size of a marathon bar. I take it its not in the centr cubby, thats where most live.
The unit wont work without it. Try R35LEE for a replacement, I would hate to think what Nissan charge. Also, if you get one carry spare batteries.