There's actually a forum post on here from the creator of said mod. He recently posted a link to the newest version in December of last year. https://www.halo2.online/threads/co-op-mode.434/page-2
I don't believe the old version works on newer versions of Project Cartographer, so be sure to download the new version.
EDIT: I want to note that I don't believe it's in active development, nor do I think this new compatibility release actually adds new features. I think it's just a compatibility fix.