Navigation System
 

I am considering changing to 2002 ES 300, but in Canada Lexus is not offering a navigation system for the ES. I checked with Lexus Canada and they tell that they have no plans to offer it in the future either.
Since I use the car a lot for business a navigation system would be most useful. Can anybody advice if a retrofit or a stand-alone system is available for the ES and how difficult is it to install.