Now that I'm reading the comments about the difficulty in cutting, that answers a question that arose while replacing the worm gear in a truck with Lionel's original magnets. Both magnets appeared to have been cut in a very jagged fashion, and I wondered why? Brittleness and difficulty in cutting could certainly explain that!
Well, all that said, I wonder if I could stack up and JB Weld a small pile of the "button" neodymium magnets to accomplish the same end? I wouldn't have the luxury of being able to adjust the "length" of the stack, but I could get lucky, and get close to an exact fit.
Just saw Pete's comments while typing this - good suggestions, think i'll give it a go!