The MITSUBISHI - SATOH TRACTOR INFORMATION, PARTS, AND SUPPORT.PDF has finally been updated. It's no longer in that difficult to read and no possible to search older PDF format. Edwin Krampitz wrote the first edition. He did a fine job at it. However, Ed Krampitz tractor historian passed...
Try to look up FridayParts, brake discs, pads, and calipers are available. if it is difficult to get, the staff may help you find the parts. I browsed its website, the boss made a name for himself in this business, it seems, by finding a generator for a customer that was impossible to get elsewhere. So, you might want to give them a try.