So I was going to suggest Suzy Cream Cheese as a pollen plant, but see that you've already used i.
I don't know if you have access to the pollen of Barbara, but she as well as Suzy Cream Cheese, are two of my very very late bloomers here in my 5B-6A zone. They both go well into October.
Genesta and Late Summer Fling are two others.
I see to, that you have used Final Touch. Bud builders are another way to extend the blooming season.
