Both the vocative and the locative are pretty rare cases, and not found in all kinds of words. Is there any word that is attested in both cases in classical Latin? I prefer the vocative to be distinct from the nominative, if possible.
I can easily conceive of situations where those two cases might arise, but I'm not sure if it has actual ever happened in the literature. The two attestations need not be in the same work or the same author.