Fall planting is definitely the best time to plant most things. However, the nurseries try to clear everything out in August and won't re-order because it is so difficult to keep nursery stock alive in the heat, so it is very frustrating for those of us who share your mindset, at least those of us in zone 8 in Central Texas.
I can't even imagine trying to deal with nurseries in Texas heat! All I can suggest is mailorder from somewhere in the East - like Bluestone - who is clearing out their spring/summer inventory in the fall. I know that's expensive!