You most likely won't find it listed in the seed catalogs. There's been a lot of negative publicity about comfrey, and it's on the naughty plant list. IMO, it's just more of the same bla, bla, bla, from government and folks who want to keep us dependent on processed animal feed. I got mine from Coe's Comfrey. I doubt that it would be happy in a pot. The stuff has a massive root system, and mines minerals from 10' deep. Keeping it in a pot would be counterproductive to the benefit provided by the plant. Coe sells a Russian variety that is sterile.