@ConquistadoR I too think that all admirals likely have CoC of some sort, since they have fully mastered their DF powers, maybe just not as potent as Garp's, since he is focused on his natural power and Haki. Because if Broccoli-Man had no CoC at all, guys like Garp would wash him, Akainu, Aokiji & co.
As Chinjao said, the seas are full of those with the Haki of a King and Rayleigh too said this power can often be found among those who have made a name for themselves. We know that high tiers like Doffy, Katakuri and Hancock have it. But the strongest military force does not? Fujitora and Greenbull were also labelled as power houses and the ones picked in the world wide military draft.