Giant Marsh Marigold

I have asked before but maybe a new member to GC might give me some information re the above. Asking for a friend as I don’t have a pond altho I do have a wee burn ( stream to you lot down South)that runs through my garden and there are ordinary Marsh Marigold that grow on the banks.


My neighbour promised me a chunk of their giant which used to be spectacular but not being gardeners they forgot to water it ( was in an old tub) and most of it has died and I never got a section.
Does anybody know how easy it is to grow from seed? If buying seed does it need to be fresh? Happy to try growing some myself but have zero knowledge of the plant. All I do know is if grown successfully it is spectacular and flowers for ages so would like to give it a go.

 

Couldn't find anything in Chiltern's catalogue but the RHS list some suppliers....Expert help & tips on garden & indoor plants | Plant finder & selector / RHS Gardening

 

I've never grown the giant one @hailbopp , but I expect it wouldn't be too difficult from seed if conditions suit, and if that's a viable method. I've never looked into it though.
We used to have it everywhere in a previous garden - the ponds were fed from a natural spring further up.
Perhaps it would be easier to buy a plant, and then you can divide it later for more. Placesd like Puddleplants stock it
I only grow the white one here.