What Evenston said.
There is no 'module' to replace, unlike in some Detroit built cars/trucks, where you can easily swap out the ignition control module, complete with new keys (car/truck thieves love this Detroit-built feature). The i3 instead has something like ten key codes, tagged to the VIN, hard-coded in the car's main ECM at the factory. The Dealer can order you new keys from the factory, that will use one or two of the unassigned key codes, and provide the new programmed keys if you supply them with the VIN and proof of ownership. You might also have them de-activate the two key codes for the missing keys so they can't be used to start the car. (New keys won't be cheap - expect them to be in the $500/$600 range - but there is no other way to get them).