Rudy, it would greatly help us find what your looking for if we knew the context of what you want. "Peace" is an English word; the Japanese have multiple words/characters that mean different aspects of the English term.
If you're just looking for the character for peace used in the phrase "Art of Peace", I'm afraid you're out of luck. The "Art of Peace" was simply Steven's ostentatious rendering of the term "aikido". If you're looking for the term and character most often associated with martial arts and peace from conflict, that would be 和, wa.
That clears up a bit of my confusion and seems to support Jun's post which points to a direct quote from OSensei「和合の道」("wagou no michi") as coming closest to the English phrase "The Art of Peace".