Honestly he's gone so long without anything even remotely resembling proper bird food that scrambled eggs (not raw) tonight/today and chicken starter if proper waterfowl food cant be found would be better than nothing/what he's been getting. He's at the point where he cant wait for perfect - get...
Nothing you're feeding him is appropriate for a duckling to actually live on. He needs real duck food. I don't know where you're located so I don't know what brands are actually available to you, but Mazuri is arguably the best...