It's a difficult one. There's a UK knapping forum you could try. You'll find it on a search engine. If you do find a source let me know. I'm running out of flint fast. Norfolks along way for me also, traveling from the midlands. I've got a couple of pure nodgules that I'm afraid of cracking open, Just in case I mess up :yikes: I've just returned from the Lake district in search for knappable stone also. I came back with some green stone that we once made polished axe heads out of.
Let me know how you get on.
Best wishes,
James