Comfrey root is available for sale in the Netherlands (https://www.anniesheilzamekruiden.nl/default/smeerwortel.html?gclid=CjwKCAjwuIWHBhBDEiwACXQYsWS9yte_1jyAZ6XVyJJm5_Dja31zNYMzrmHrrgClGLmMOFKihBTbNBoCEBoQAvD_BwE#145=6), despite the fact that in some countries it is illegal to sell it for human consumption. I have yet to try locating and foraging some myself, but considering its toxicity to the liver, I think it may be better for a beginner forager like me to start with safer plants first.
Urban Herbology Apprenticeship
Foraging, Growing and Using Herbs in Cities