sly-documentation-lookup-function is a configurable variable that holds the function that will lookup documentation for code in the hyperspec. It currently defaults to sly-hyperspec-lookup. The implementation of sly-hyperspec-lookup lives in lib/hyperspec.el and it is an alias to common-lisp-hyperspec.
I'm proposing to create a new module in lib called community-spec.el that will contain the implementation for the sly-community-spec-lookup function.
Since the community spec has a JSON listing, I'm proposing to maybe parse that?
https://cl-community-spec.github.io/searchable_terms.json
Another possibility is to contribute a dynamic JSON API for the community spec.