@dickwad Nadroji Ring & Amulet can be found above floor 100 of any difficulty level from defeating Epic+ monsters, not above floor 250! the Chest & Head Nadroji are found above floor 200 from defeating Epic+ monsters on Epic+ Difficulty.
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@kowiz if you don’t have Amethyst Crystal, you will be stuck with Nadroji Set. but that is good since you can use it for farming for the better chance to find Rare Legend Items. or Convert enough lower Myth Stones up until you have two Elixor Myth Stones so you can put the +2 All Sets in any Ring/Neck Item you want. or even replace Nadroji Set with another affix that you think is better.
as far as the Set to choose, read the Codex > Dictionary > Sets, and see if there is any that you would like to use in your Build. then look in the Codex > LegendEx to see which items have the Set you want, or look at this post…
to find the right way to get the Set you want.
for now, replace the Deadly Arts affix with something else until you find a Nadroji Ring.