The Turkey Head costume is a limited time only costume. If you want it, and haven't already bought it, then you have to wait until around the time of Thanksgiving to get it.
Thanksgiving
The Sephiroth costume came out on July 13, 2011 for LittleBigPlanet 2.
It is a costume for Littlebigplanet 2 that you buy from the Playstation store for $1.99 or 5.99 as part of the LBP2 Final Fantasy VII Costume Pack.
It will not be out. The Final Fantasy Costume Pack and the Individual costumes are only for LittleBigPlanet 2
You cannot.
You have to ace the three Savannah levels to get the full costume
It is only out for LittleBigPlanet 2 both as a separate costume for $1.99 and part of the Final Fantasy costume pack for $5.99 at the Playstation Store
If there is a contest on, it will probably give you an option to submit your costume
buy it from the PS Store
You purchase it from the PSN Store.
You can only get it at cristmas
The Pumpkin head is a Halloween costume, meaning you'll only be able to download it around Halloween. If you've already purchased it, then you can download it any time you want, though.