Hmmm...what do I have lying around the house that can be used to make a doll's stethoscope? This is a problem-solving adventure and work-in-progress, so check back!
Step 1: For the tubing, I sacrificed a bit of USB extension cord. I hope it wasn't important. For the ear tube, I used some of my armature material - 14 gauge aluminum electric fence wire.
Step 2: Now to figure out how to attach the wire (tubing) to the ear tube. I used a #11 scalpel blade to split the wire casing on each side - a little over 1/2 inch in length.
[Stethoscope #2 - don't need to split the casing on two sides to remove the inner wires - one slit will do]
[Update, see Step 11 below]
[Update] Next time I'll do this to remove the wires before making the slits for the wire ear tube insertion. This should make the connection between the main tube and ear tube more secure.