Regarding the 1938 novel by T.H. White:
If copyright was renewed, it will enter the public domain in 2033.
If copyright was not renewed, it is currently in the public domain.
Regarding the 1963 Disney film:
No.
No; they will be protected for the life of the author plus 70 years.
The sword in the stone is nobody, it is a model. There is a legend of a wizard named Merlin, to help king aurthur seek the sword.
In terms of intellectual property "public domain" refers to items that have no restrictions of use due to expiration of legal controls (patents, trademarks, copyright)
How many swords do you find in a rock? Of course its no ordinary sword!
excaliber? the sword was not officially named in the movie but being a story of Merlin and a VERY young king Arthur it is safe to guess excalibur.
E3 2010: The Legend of Zelda: Skyward Sword E3 Trailer
E3 2010: Swords E3 Trailer
Sword
The Legend of Zelda: Skyward Sword Demo 2