The RVL vocabulary can be downloaded from GitHub.
You may also directly retrieve RVL from its URI, which is dereferencable and will return the ontology as application/x-turtle if you do not explicitly request text/html (which will show you the documentation).
So opening http://purl.org/rvl/ with a browser will show you the documentation, while requesting
curl -L http://purl.org/rvl/ -H "Accept: application/x-turtle"
will give you the vocabulary in turtle serialization instead. Let us know about any problems you may experience accessing RVL with other user agents.