You may have to special order the 8 foot high door, but when the big box stores are having a door sale, the special order sizes are usually on sale also. It's not that expensive.
As to the Pella door referenced by Eddie: I have a couple of Pella doors from Lowes and they work OK after installation but it was a nightmare. They were shipped with incorrect parts, they are considerably lighter than comparable Cloplay or Ideal doors, and just didn't seem as well made. That said, I've had them installed for several years and haven't had a problem once I got them in. I forget the actual name brand now, but they were third party - the name Pella did not appear anywhere on the doors or packaging.
Interestingly enough, I bought them because they were the only doors I could find prefinished in brown to exactly match my Andersen windows.