Navionics are no longer available as of this past March I believe. Generally speaking your local dealer is the best place to get your map unlock codes.
If in North America, Contact Tech support via our website (www.FurunoUSA.com) under Support - Ask a question. Provide the a Lat/Lon for the area you are asking about and they can help you with some example screenshots of options. If you are outside of North America please directly contact your local Furuno distributor.