Certified copy?

You got married in a Church of GEP in Las Vegas. What the fuck use would a certified copy of the certificate be.

Seriously but, there's loads of people who can certify it for you. Including but not limited to

A Lawyer (or Notary Public)
An Accountant (with a recognised qualification)
Serving Policeman or Customs Officer
Senior Civil Servant

They need to write that they have seen the original documentation and that this copy is an accurate and complete copy.

They need to sign and date it.

Put their name, address and position in block capitals.

If they have an official stamp they should add that too.