Install cet-standard LaTeX document classes and style files

The memarticle documentclass, and several supporting packages, are available via a tarball for installation in your own texmf tree.

If you have a TeXLive installation on a Mac, this is located at ~/Library/texmf and the directories therein.
Get the tarball:
Put the tarball in your ~/Library/texmf directory, and unpack it:

tar xvf cet-latex-pkg-v1.0.0.tar.gz

It is a good idea to also periodically update your LaTeX installation. For a TeXLive installation, this is done with:

sudo tlmgr update --self --all