Lucky Egg only has a 10% chance of appearing on a wild Chansey (and no, you can't breed a Pokemon with any sort of item, it would be too easy if that was possible). I've not found one yet, but I've not been looking (and only caught 2 Chansey, second one was for my friend. Neither one had a Lucky Egg).
Just be patient and one will show up (I was having the same trouble getting a Dragon Scale to evolve Seadra into Kingdra, since that only has 10% chance of appearing on wild Horsea, I gave up looking and won the Double Battles in the Trainer Tower (north of Seven Isle) to get a Dragon Scale).