there is a way you can make copies of your pokemon in goldbut gold only.
follow these steps:
1)clear out box five and six
2)choose the pokemon to be duped
3)put pokemon in box five(not for special reason)
4)Change to box six...and when it says SAVING DO NOT TUCH POWER BOTTON switch the game of
5)start the game back up:there should be the pokemon you wanted copies of in you team and in box five
6)enjoy!