I don't know how eggs are in your country but, here, we can get medium, large, extra large and jumbo eggs and the medium ones are very similar to a macaw egg.
Yes, Birdwoman, you are 100% correct but the OP is in Sweden or Finland and the bird has already laid the egg so I figured that the fastest thing would be to use a chicken egg to replace the real one.
Sometimes they will have them at the grange or a feed store , but over there ?????? Do they farm or is it to cold ? Ignorant about other countries B.W.