While if you call C-map, they can sell unlock codes; most codes are purchased from your Furuno dealer. They will need to know the area and type of chart you wish to purchase and the system ID number from your unit. Chart options can be found by look at the Furuno website under "Discover Products - Browse all products - Charts for NN3D, TZT, TZT1, TZT2, and TZT3"