I suspect it hasn't been featured on any gardening shows. So doesnt have a high profile so gc don't offer it. I have seen it before in a friend's garden in Shropshire. She bought it from a specialist grower.

Can't find anyone that sells it by seed or in shrub form in u.k. ventor botanic I.O.W sold it at one time they are the only ones on plant finder. It's more popular in u.s.a