You will find the mercurial repository for the Coco ROMs located here.
For those of you who don't know how to use mercurial, you are strongly encouraged to read the mercurial documentation. However, the following should get you started if you have mercurial already installed (assuming a unix-like system):
hg clone http://cocoroms.projects.l-w.ca/hg cocoroms
Other files of interest are listed below.