How do you register new pokemon on the 3d pokedex?

How or where do I get the codes to add new pokemon

Every player gets diffrent pokemon at the same time. For example, say one of your starters was Pansage. Another person who has the pokedex will get a diffrent starter. Currently i have no idea how to unlock more. But, if you know someone else who has the pokedex, then, theres a button you click to get them from a friend.


Hope this makes sense!