As I understand it, they actually all but lost the Norfolk Horn and had to recreate it from the Suffolk and Southdown.
Some spinners in one of my local groups had some of Adam's Norfolk Horn fleece a couple of years ago and said it was awful!
But I have had two lots of Nofolk Horn; one lot last year was passed to me to spin the yarn for the Norfolk Horn for the RBST Rare Breeds Heritage Blanket project. I absolutely loved it, and wanted more, so bought a fleece this year, which is just as nice as the RBST sample.
Norfolk Horn is one of Deb Robson's favourite fibres, too.
I know there are flocks in the South East, Rampisham for one, but as you say, MF - that might be pretty much the entire National clip for this breed!