Can you clarify what you mean by "spec"? The bitcode ABI document I pointed to is the spec of the IR used by PNaCl. The official documentation covers the Pepper APIs which are PNaCl's interface with the browser and DOM.
A document with which someone could create an alternative implementation; like another browser for example. Do I take this to mean that there isn't one?
There is no real "spec" of the Pepper APIs, just API docs. While those might be of high quality, it still depends on many implementation details, so it seems like it would be challenging for another browser to duplicate.
