I don't think it's the sort of thing the average Garden Centre would sell, so you need to find a specialist supplier of wild flowers. There are several mail order suppliers of British wild flowers and seeds, or you could try Ebay.

hiya

there's plenty to be seen around the outside perimeter walls of your local allotment site (if your not a lottie holder) so you're able to dig some roots up and plant it in your garden. it's v invasive tho' so unless you have the space for it, then i'll happily grow away for you. here's a recmd nursery - herbal haven nr saffron walden, essex. i've been to their stall a couple of times in local green events and garden shows this yr. they're v knowledgable and friendly and their plants are only £1.50 and del. costs v reasonable too. hope you'll get some growing soon. it's an amazing plant. i've got mine harvested from friend's lottie and am making comfrey liquid as a feed.

You can order Bocking 14 comfrey from the organic gardening catalogue - 10 slips for £7.95. This is the best comfrey for making comfrey tea or using as a garden fertiliser or mulch - you can get 6 harvests a year. Tough stuff and worth getting.

I have five rows of wild comfrey and two rows of nettles grown properly with weeding and hoeing. I got mine by looking around the allotment site. They grow in the hedges and waste areas.
I am also using sweet cicely which also makes a good liquid fertilizer. I harvest them by cutting near to the base of the plant and take off all the leaves. They are then put into one of two very large butts I have. I do not add any water, although I have made comfrey tea using water in the past. I leave the comfrey, nettles and sweet cicely leaves in the butt for about a month or two. However, I keep draining off the tea using taps at the bottom of the butts and putting into the dustbins with charcoal.

The tea looks just like Tomorite to me. I keep filling my butt up with leaves throughout the year as they rot down. I try not let the plants get too big or flower. I harvest the leaves about 5 times a year putting the leaves in the same butt unless it is full. I have other butts that I can put comfrey in if I have too much. There is a tap at the bottom of the comfrey butt and I use this to put some in the watering can each time I water things. It is relatively high in potash (K) - good for flowers and fruit. So, yes you can keep adding leaves to the butt if you want to.

They say that nettles are high in nitrogen and comfrey is high in potassium. Compared with what though? I think we are talking about very small amounts of nutrient but that is all that most vegetables seem to need. Nettle and Comfrey have more nutrient than farmyard manure but farmyard manure has very little nutrient in, so it does not need much more to be better.

Ken Thompson in his book "An Ear to the Ground" says that Russian Comfrey Symphytum x uplandicum is rich in all three main mineral nutrients, nitrogen, phosphorus and potassium but it is not unique in this. "Some plants can do just as well, maybe even a little better including: chickweed (Stellaria media), nettle (Urtica dioica), sweet cicely (Myrrhis ororata), fat hen (Chenopodium album), goose grass (Galium aparine), and hedge garlic (Alliaria petiolata). So I chuck some of these into the butts as well.

I think that the adding of both comfrey liquid and farmyard manure have greater effects than just adding nutrient to the soil. They encourage soil organisms which may form symbiotic associations with plant roots or at least provide further nutrients or nutrients in a form that the plants can use.

Healthy soils with lots of dead plant matter, humus and microorganisms grow good plants.

Comfrey is as tough as old boots. It will certainly come back in the spring. Mine has died completely back and is difficult to make out at the moment. I tried digging between the rows and started to dig up roots. Not to worry though because I just planted them again. They might not come but I have sufficient anyway.

A bit of frost and snow will not hurt comfrey.

Here is a link that might be useful: