This is a code someone at
mickorola@aol.com sent me its a working code for Punch Out! I didn't think it would work till I tried it, but the thing worked here it is the draw back is you need to make a new town for it to work so use a spare memory card then take the game over to your main town.
First, start a new town called Tzu and name your character (space)Lao. Note that it isn't actually (space), it is a single space before the name. Do all of the work for Nook so you will be able to tell him a password, the password is: 3Ec5za9xYcxkLm yYR9ryOz%ucJ6V
Tom Nook will say Ah, yes you entered your name in a contest to win an NES game,eh!
I see, I see. Here is your Punch Out.