Is it possible to get Mew on Pokemon: Explorers of Sky?

Yes it is. All you have to do is once you have completed the game you go to the juice bar place and talk to the Pokemon standing at the doorway it may take a while for it to finally be Mew but if it is you go to mystifying forest and battle Mew hope I helped

You can also use this Wonder Mail it will be on F30:W4H=2 C0MWX# SC4KF
9K@@Q @&5N3Q2 3@338

-----EDIT------
For Some Reason i think i gave you an (S) WM so if doesn't works please tell me ok?...

Yeah. Go to the end of mystery jungle. If you don't get Mew, keep repeating. You will also get a grass cornet if you beat Mew.

To unlock Mew Here is how you do it.

After yo uhave completed the main game, after some time, you will see Mr. Mime, standing at the cross roads, where spindas cafe and stuff is.
He will tell you about Scizor. The amazing explorer that was lost while exploring Blizzard Island. Then, you will unlock Blizzard Island. When you reach the end of Blizzard island, you will unlock yet another cave. Crevice Cave. At the end of that, you will see a Scizor frozen solid. A frosslass will then battle you. After that, he will thank you, and scizor will grant you access to "Secret Rank" which allows you to get special missions. The missions will appear at Spindas cafe. Someone will be standing at the door, and will give a mission. You Want the one to gain access to "Mystery Forest" (Something like that) At the botton, Mew awaits. Defeat Mew, and you have a slight chance of recruiting him on the first try. You may have to go down a second time, but the second time he will join you. Hope this helps!!