Luckily for all Duck Hunt fans it does indeed exist for the wi!!
You'll need to download the latest FCE Ultra emu for the wii via the Homebrew Channel. Once installed put the Duckhunt rom in the correct folder and start it up. You can even play with a targeting reticule on sceen to help zap em!
The Wii FCE Ultra is by far the best NES emulator I've used on a console. It's so sharp and clean and having the wii remote pointer work is just icing on top of the cake. The coder/s really did a bang up job porting this to the wii.