There's no cheat to get the national dex,but if you go down in the action replay you should se a sign that says "Pokedex 100% complete (L+R+select) put a check on it now go to your game and press "L+R+select" and you should have completed it and you can get the national dex,after you recieve the national dex you have to start finding new pokemons or just do the cheats again but might messes up your game. Hope this helps you.

By:themaster1998123456 "themaster or master for short"