As with many other automotive accessories, you may want to start by contacting the manufacturer of your vehicle.  In some cases, if you are buying a new car, you can choose to have a car dvd navigation system installed.  That said, if you own an older vehicle, you can still find a suitable device in a local electronics store.  If you cannot find a  model that suits your needs, it may be best to search online.  For the most part, you will have a large number of models and manufacturers to choose from.  As may be expected, once you start researching these devices, you will find all kinds of uses for them.