Pommel - Level -49: In the top left cell of the prison, there is a wall that you can use a Magic Mattock on to reveal a secret passage "tunnel". It is the farthest wall to the left in the cell.
Guard - Level -49: In the top right cell of the prison, there is a wall that you can use a Magic Mattock on to reveal a secret passage "tunnel". It is the second wall in from the right in the cell.
Blade Fragment 1 - Level -50: At some point in the 5th Zone you will pick up a Scroll of Depth, return to level -49 using your wand of flight and use the Scroll of Depth. You will be teleported to level -50 where you must use a red key to open a door and defeat a big blue dragon, once slain that dragon will drop the Wand of Frost. Use the wan to cool the lava and the blade fragment can be picked up in the top cluster of items.
Blade Fragment 2 - Level -6: In the 5th zone once you reach level 7 use a Scroll of Height, it will transport you to a hidden level 6 that contains the Elder Elder, who has the final piece of the Fire Sword and a salesman that will give you 2000 Gold, as well as some miscellaneous items. There are two Fire Elementals that you must defeat in order to open the doors.
Return with all your bits to level -35 and use your Wand of Freeze to access the forge Dwarf. Choose the Fire Sword option and he will make your sword for you once you have all of the pieces.