I think you need to look for Rudbeckia maxima.

Here is a link that might be useful: Rudbeckia maxima

Good on you florauk. According to my perennial books, Rudbeckia maxima is the botanical name altho' they're not an Echinacea as are coneflowers that are traditionally referred to by that name. Rudbeckias are normally lumped into the 'brown-eyed susan' family rather than coneflowers altho' the flower form is similar.

If they're anything like the ordinary Rudbeckias growing where I am, they thrive in full sun, heat, & dry soil that isn't necessarily rich in nutrients.

I checked Hazzard's Seeds' website and they do offer them. You might also check Swallowtail Garden Seeds. I offer those seed-source suggestions merely because I've had good experiences with both.

If you grow them from seed via winter sowing, it's generally a good idea to sow the seeds in spring since (according to my notes) the seeds don't need a cold period in order to germinate. If you don't want to go that route, you might check your local nurseries when Spring rolls around altho' I can honestly say I've never seen them for sale where I am, I'm guessing because my growing season is much shorter than where you are. I have no experience with open sowing them in the ground.

Best of luck to you!

All I did was Google Giant Coneflower and up it came.

However, Echinacea is generally called 'Echinacea' (!) here and Rudbeckias are occasionally called cone flowers, so I was thinking along those lines anyway. The seed is available from the place I linked to also.