Those parts are specially customized for the Niryo One so from what I know, it’s not possible to find them on online seller.
A process of selling individual parts at details is in creation, it will be soon available (within 10 days) to buy only the parts people really needs and not the whole “Maker kit”.
It will only be available by email at first (will be later added to website), so I gave your gmail address (Bruno) to the people in charge of this, he will contacts you with the details on how to operate if you’re interested in buying those parts individually.
I hope it may help you.
PS: For other people who may be interested in buying specific parts, please contact this address: firstname.lastname@example.org