They still turn up every now and again in old established hatmakers dead stock to this very day.
You better believe it! Bout 3 years ago, my bud Sharpetoyes found a little known hatter up north. A Greek chap, past retirment age, who had mercury bodies in the basement of his retail hat shop. He mostly sold factory hats, but would make you one, if you wanted. Sharpetoyes I think bought every vintage mercury body the guy had, in the form of a hat. And, he stole them, pricewise. The old hatter's name was Gus. I think. Boy would I love to spend some time in his basement, with all of those old blocks and hand hat tools. It would be like a museum experience, for me.
When Sharptoyes asked what grit he used for pouncing hats, old Gus said 320. If it was good enough for his jeweler friend, Gus, says, its good enough for me! So, it seems the real fine grits were not used much in the old days, if you can trust Gus. And it appears jewelers use this grit in grinding their stones. I thought it was funny at the time, due to the 2000 grit hats being advertised. But in the end, the grit used is determined by, (1, the type of felt, and (2, the finish you are working towards. Gus probably wanted to feel the nap on his hats. And there is some felt that even a 2000 grit won't clean up. Nothing will. Garbage in, garbage out. Fedora