The nectar is one of the many important artifacts of Hades. This item is required to access the Memories, Companions and Romance options of NPCs. Nectar is one of the easiest artifacts to find, but it can still be hard to find when you need to get that last memory. Here's a quick guide on how to get your hands on a lot of nectar.
Miserable broker and Charon
The Miserable Broker has everything you can think of to meet all of your shadow destruction needs. The broker's shop should be checked after every run to see what they have in stock. He sometimes sells Nectar for five Chthonic Keys in a Repeatable Trade, or for 10 Gems in a Limited Time Trade.
Charon will also occasionally store Nectar in his stores for 200 Obols. Keep an eye out for him as you explore or use a memento or entrepreneur upgrade to spawn him more frequently. Farming Obols is very easy thanks to the Night Mirror perks and Entrepreneur upgrades, so grabbing nectar or other valuable items from Charon should be pretty easy. Don't be afraid to spend those precious Obols when you see it.
Advantages
There are two perks available that can give you bonus Nectar. Poseidon's Sunken Treasure offers you a set of currency items. Sunken Treasure has a 10% chance to also grant you nectar. Dionysus' Vintage Premium Perk will give you a bit of extra health each time you pick up a nectar and drop one when you choose. If you like playing with Dionysus or the benefits of Poseidon, these will be easy to find. You can also use their memories to have a chance and get those benefits early on.
Exploration
The absolute best way to get Nectar is to simply explore the Underworld. The nectar is a possible drop at the end of each chamber. Once you've completed a chamber and you have to choose where to go next, go through any door with the gold-colored bottle of nectar floating above to ensure a drop in the next chamber.
You can also earn nectar by completing Hellish Treasure challenges. There is a five percent chance that each treasure will drop nectar, but you can increase the chances of a treasure spawning through upgrades at the house builder. You can also purchase a Trove Tracker item from Wells of Charon which will make it easier for you to find Troves.