External vocabulary services are defined in the graph http://vitro.mannlib.cornell.edu/filegraph/abox/vocabularySource.n3. You can explore the contents of this graph by navigating to System Admin / Ingest tools / Manage Jena models. Find vocabularySource.n3 in the list of models. Click Output Model. You will get a file containing the assertions made to define external vocabulary services in your VIVO.