Where do you get Save The King plus in Kingdom Hearts 2?

Answer 1

The same place you get the regular Save The King - the Synthesis Workshops that the Moodles run. When you synthesize Save The King, you'll be able to synthesize Save The King+, which is identical except that it has the MP Rage ability instead of the Item Boost ability.

Of course, to synthesize the shield in the first place, you'll need the Recipe. The King Recipe is found in Port Royal (Pirates of the Caribbean: The Curse of the Black Pearl) in the Seadrift Row of the Ship Graveyard, which is only accessible on the second visit, after Luxord destroys the Interceptor.