You need to defeat the dragon on level 50, get two more parts from level 49 (the rogue on level 6 gives you the clue of where to dig - you will need 2 pick axes or an earthquake spell), and the fourth part is given to you by the Elder who tells you about it. Take all four bits to the dwarf smith on level 35 and make sure you don't ask for the wrong thing as he will either give you +100 Defense OR reforge the sword once you have the parts, but not both). The Ice Wand to soldify the lava is got from the dragon.

To get to the dragon you need the scroll of depth. To defeat the dragon you almost certainly need the gauntlets from level 3, which takes a couple of teleport scrolls to get to, plus you either need to be able to defeat at least one of the elementals guarding it, or have a bomb.

Thanks sfnhltb!

Thanks again sfnhltb! And thank you for the great guide!