Via local (Netherlands) Canyon support I (think/hope I) ordered the low version of the nutrition box; apparently you need two parts, the rubber outside and a plastic internal box.
One of these parts is labeled: CAYN Storage Shell E431-16
other one I don't know (I don't see the item-nr in my order status, just that there is an item)
combined price is around â‚¬15
Items are not in the webshop, so I would advise to call your local support team.