Coby is definitely getting acoc. Law had his chance of unlocking it when he fought three yonko in a less than a month. If that does not cause it to bloom, nothing will.
King didn't need it. He's part of the most OP race in the verse and outside the race isn't important enough for acoc.
Y'all need to realize that before Alvida Coby was a normal kid. He wasn't getting his ass beat by his father and his goons, or training non stop in a dojo, or surviving the woods with his bros for years.
Once Luffy gave him his balls he's had godly willpower