Each of these organizations have lists of coaches that have been certified to some degree. I have no idea what career coaching certification actually means, but I found my coach in this way. Each of the programs have search pages where you can look for a coach based on your requirements, location, etc. Once you get some names, you definitely need to give them a call and have a 10 minute conversation getting a feel for their "style". Most coaches have info on their websites or that they will send you that attempts to give you an idea of how they work. In particular I would pay attention to how much a coach follows a socratic method (i.e. just asking questions and guiding you) vs more training oriented (i.e. you need to do x, y and z). Good luck!
To motivate you? Friends and family can do that.
To teach you a skill? Try connecting with someone through SkillShare.
To hold you accountable? Ask your colleagues and peers.
A couple of the suggestions above rely on getting feedback/advice from potentially biased sources. If you're serious about an actual coach, have you considered hiring a professional life or business coach?
Again, how are you looking to improve yourself?
HN community is my second Coach.
My email address is in my profile.