There are various body parts around. I have a set of intestines, a heart and a brain, all scavenged (uhm.. bad choice of words I guess) from various free sites over time. _dodger made a brain, EllPro made the heart and I can't remember who made the digestive system I have but it looks ok stuffed inside the old Poser skeleton L

That said, those are all years and years old, and I don't know if they're still available. Have you checked free stuff here? I'm pretty sure that's where I got the heart at least :)

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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.