1. Zoro had CoC focus in the anime where he first used it to knock out beast pirates in the dining hall, oda most likely just didn't have the time or space to put it in the manga.
2. It hasn't been confirmed that King doesn't have CoC, but it would be very plausible to think why he does. first, katakuri already has it, why wouldn't King? Second, his name is literally King, and the all stars are ranked in strength as they are a meritocracy, if anyone from the all stars has CoC, it would be king. Third, what is the point of Zoro using CoC in his fight with King if King himself doesn't have CoC? Kaido even implied that Zoro has actually gone a step further and can already imbue CoC into his swords already, as Zoro was able to permanently scar Kaido. if King doesn't have CoC himself then how else can King vs Zoro be a extreme diff fight??
3. The very existence of Enma as zoro's training tool is pointing towards him training his CoC in his fight with King. Right now Zoro has already exhausted his CoA haki, he was already tired before from his fight with Kaido and blocking Hakai. And because of his lack of armament haki, enma is going out of control and sucking up his energy again. CoC Haki is the only haki Zoro still has left in reserve to tame Enma.
4. If Zoro has run out of CoA and needs Adv CoC to beat King, then King also needs CoC at the very least to to match with Zoro to give Zoro a extreme diff win. If King doesn't have Adv CoC how else can King push Zoro to extreme diff? King has already shown most of his trump cards already-hybrid, Lunarian flames, tough body etc, CoC would be one of the last remaining trump cards that King still hasn't revealed yet to compete with zoro
