Comfrey contains symphytyme and Pyrrolizidine Alkaloid which both impacts the liver.
I checked it and on Etsy you can buy comfrey root and also in some bio-webshops. I also bought a muscles-and-joints tincture at the ecostore once when I had an injury from bouldering and it contains comfrey. So it is possible in the Netherlands.
Comfrey-ointment was the first herb-product I ever made, a while ago already. Now I make it regularly as working in the garden can cause wounds easily.