Diffuse is usually just the plain texture map :) You should be able to find that in the runtime/Libraries/Textures folder - unless of course, you've put something on from another location.

There is/was a script to collect everything used in a scene into one folder. My Poser's rendering atm so I can't check if it's still there - or for that matter, if it was some external one I got at some point :( But check for something like Collect All :)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.