First Of all, 500k hp is nearly imposible without nadroji's stone, nadroji's crystal/frightening choker and 2 Elixer mythstones. You would need to stack plagued with other hp-boosting set affixes. Not sure if that's entirely worth it.
As far as Nadroji and Frightening choker go, I have been to floor 575+ on easy difficulty and seen nothing. Been through 2 ascendtions, took Dealer and The perk that boosts luck/goldfind/pickup radius. My luck is over 700% boosted, and I run 200+ packsize maps on mythic 1-2 no problem. Never seen the choker or a single peice of nadroji gear. I got impatient and stuck an elixer on my ring. I get farming... I do... but I think some items are bugged.
Either that, or I am simply hot patient enough... although when I have spent over 100 hours on the game and farmed on my off days... not entirelysure I want to be "patient" for months. I give up on those peices. Im building reactor sets for my other toons.
Oh, and if anyone HASNT bought the premium stashes yet... do it. Best decision next to the Auot Map Reveal. About as useful as air.