I don't know if you are asking about Capability Maturity Model (for software organizations) or the People Capability Maturity Model (for any organization).
There is no certification for either. There is a way for an organization to do an appraisal of their capabilities against these models. The best way to find organizations that do these appraisals might be to check the website of the SEI and use the quicksearch to look under Lead Appraisers.
www.sei.cmu.edu
I have done both, but today focus mostly on informal diagnostics and P-CMM appraisals.
Best Regards,
Bill Hefley