The Concise New Partridge Dictionary of Slang and Unconventional English (google books) gives the following sense of bark:
the skin noun 1758 UK
My sense of hard bark on someone would be akin to thick or tough skinned. I think the usage of bark=skin pre-dates the cinematic era as posed in you question, but I too cannot find any reference to hard bark that predate the cinematic era other than those you posted.