Hi Nick and Sal
Russian Comfrey is normally propagated by means of offshoots or root cuttings, from which it grows like mad! There are a number of strains and the one known as "Bocking 14" is reputed to be the best . You can easily take offshoots from a friend's plants or order direct from Garden Organic at Ryton, UK (
www.organiccatalogue.com). Comfrey is rarely grown from seed and this could be because the selected strains are better.
Alec.