Does it have a maintainer currently? There are issues and merge requests on GitHub (https://github.com/hankhero/cl-json) that are just stuck. Should some fork take over the mantle of being "official"? Is there anyone who is willing to take this over? I'm not, sorry -- I have too many projects to manage already.
If there *is* someone to take this over, maybe they could contact the folks at common-lisp.net to transfer ownership of the project page there, and add a pointer to the new GitHub repo.