unfortunately i did not find the replacement rubber, but the complete component can be bought. I have been thinking to use a 3D print or just use a rubber strip. Did not get to it.
Part for sale: https://www.solisonderdelen.nl/nl/catego...
rubber strip: https://www.rubbermagazijn.nl/rubberstri...
After opening the iPod Nano 6th gen and trying to fix the power-button issue (a very common problem, seen all the YouTube movies about it) I have put together the device. Unfortunately it won't power up anymore, at least the screen is not working or the device is not recharging anymore. Either way, be careful, after disassembling this device might not work anymore. Delicate parts are in place. Good luck with the teardowns.