A few years ago I published an article on teaching Metrology and the journal is no longer available nor are its archives. If so, should I remove it from my CV?
You do not have to remove it from your CV. A publication does not depend on the long-term existence of the journal. If it was printed, than there is no problem, libraries have your publication. If it was online only, the national library of the country where the journal was published should have it in its repository. To be sure that readers will find it, upload the paper to ResearchGate.
See also this discussion which I started some time ago: https://www.researchgate.net/post/How_can_the_availability_of_digital_journals_be_ensured_in_the_long_term