Note: You'll need at least one blank save slot.
To duplicate good items that you find in your quest, just:
1) Get to a level with any Forge or Shrine and a Ranger Hollow.
2) Have the item(s) in your inventory.
3) Save the game as normal, then save it to all the blank save slots you have.
4) Quit the game, start up one of the games in the save slots you just filled, and put the item(s) in the Ranger Hollow of the level.
5) Do this with all the save slots you filled.
6) Go back to your main save, and take all the items out of the Ranger Hollow, you know have duplicates of your item.
7) Repeat as wanted.