I have most of the parts to restore a MkII Martini-Henry to life, and I have just bought a barrel from this source:
http://www.martinihenry.org/index.php?route=common/home
I don't know how far it is a society rather than a business venture, for there is no mention of joining it. These things evolve. But they do seem to know about parts identification and interchangeability - although I notice a wrong picture or two. My barrel, £99.95 for what they describe as Grade 2, with rear sight bed still attached, is splendid value. The bore is excellent, with fine toolmarks visible till they join the throat. there is a tiny dark patch in one groove about four inches from the muzzle, but it doesn't affect a land, and it is eight just staining or a pit so shallow that a light touch of a brush has brightened the bottom of it. I can't see a patched bullet taking any notice of it. The only thing I can see coming between it and Grade 1 would be some external pitting which would be under the stock wood, but it isn't at all bad.