Hi
You can get a new navigation DVD off ebay, last ones were 2012, not sure about your country
but if you google it there should be plenty of places that sell them
Also if you have the touch screen, which is usually standard with the navigation, you cannot remove the Nav DVD unit in the boot, because the picture for the touch screen is generated by the Nav dvd unit in the boot, so removing it will render the touch screen useless, no climate control, no cd changer, no phone.
cheers
Joe