Replacement QC35 play, previous, next buttons (*not* power button)

The play, previous, & next buttons on my QC35 fell out and I couldn't find them. (These are the three small buttons that are at the bottom rear of the right earpiece edge, broadly similar to generic smartphone power & volume buttons but thicker.)

I searched Bose, Google, Amazon, eBay, & iFixit for replacements buttons, but only found replacements for the power button (my power button is fine) — no results at all for the play/previous/next buttons.

Where can I obtain replacements?