I am so sorry to hear your grey flew out of his cage and I pray that you find him safe and sound.
Putting up the posters is a good start but go door to door in your neighborhood and ask your neighbors to be on the lookout for him, go to your local vets, pet stores or anywhere you think that someone might have sighted him and didn't know who he belonged to and told them about. Put his cage outside with food and water in it in the hopes he might see it and go in. Please don't give up for he is out there somewhere, spread the word, let it be known you are looking for him so if someone does sight him they will contact you. I will keep you and your baby in my thoughts and prayers that he is found and I hope it is very soon, keep us informed.