Naito

You use them to empower a unique ring received when completing the brewmaster quest (don't give him the fluid straight away, he will then offer gold or this ring).

"Only four unique" in the context of Deadfire is a good number, more than blunderbusses (2) and pistols (3) (and many other one-handed melee types). Blightheart is inferior in terms of damage to Dragon's Dowry, you need to soulbind it to unlock its potential and can't apparently be enchanted to Legendary quality. Three Bells Through is also inferior to Dragon's Dowry and does friendly fire (shoots in a line, hitting up to three targets friend/foe). Dragon's Dowry packs a hit when enchanted with the +50% Burn damage and has the ability to significantly raise your attack speed, costs 45k. The Red Hand fires two shots in a closer range with a incremental damage +1% per kill until rest, but it is to be found in a random event. If you plan your MC around the arquebus, Dragon's Dowry is arguably the only valid choice. It gets worse if you have Maia in your main party. The Red Hand would at least provide a solid alternative, but it is nowhere to be found.

I don't see any replayability value in a, apparently very slim, random encounter. And the point to hoard all unique items in a single playthrough is for completionist' sake: it should be almost feasible, not easy, but doable. Having all unique items is also fun to test/run any build you would like to try with the unique items. I will add that I find there is a healthy frequency of unique items, but too many unique sabres and swords, not enough variety for arbalests, battle axes, clubs, crossbows, hatchets, hunting bows and wands.

Thanks for the heads up, we at least have an answer. I did not 100% understood it: is a something that may pop up when you search in a location such as a wrecked ship or something else? Anyway, I guess we are not fan of the "random encounter".

Dragon's Dowry is just for sale (45k) at Uto's gunsmith in the Brass Citadel. No need to join RDC or anything. A bit ironic you missed it, since it is probably one of the first powerful unique item you see and start to save up gold for it The broom is on the ground to pick up in on encounter with the "Fire Giants", the wiki mentions "Map Fight against Eotens at 6'13" 46'27"".

Not yet and it’s driving me crazy. At first I just wanted this gun in order to cross off its location on my list. Now it’s become some kind of obsessive quest of mine. I am traveling through a different play through and killing every NPC in the game in order to see if it drops off of someone we didn’t think of. Don't get too crazy about it: like Dr. Hieronymous Alloy said, if it was somehow obtainable, it would have been found by now. At this point I even consider that it is not properly implemented ingame, with a small chance that it is perhaps gated behind some contrived requirements related to PoE 1 decisions. I agree about killing every npc whenever you have the chance, that is perhaps the only critique regarding the itemization of PoE 2: a bit unfortunate for RP reasons, but you are almost sure to obtain a unique item.

Sure you didn't console it in? I'm starting to wonder if it's gated behind some rarely chosen first game option. I am also convinced it is gated behind some rare and strict requirements. That or it is not implemented in the game yet (perhaps even bugged?) or maybe rewarded from one of the plagued ships.

A good leather armor, you loot it from Benweth.

I don't remember the geographical coordinates, but it is looted from a hunter/ranger in an encounter: it was perhaps related to a bounty as well!

Arguably one of the best armors ingame.

The Firethrower's Gloves are looted from a chest in the fortress of the "Fire Giants" in the Ashen Maw: it is in the area where you can meet their faction leader. At the start of that area you can take a left, central and right way: the chest is found in the right way. I don't remember all the specific names but I tried to be as specific as possible. The cloak is looted in one of the three vases in the treasure of the "Magma dragon" in the Lair of the Ancients in Ashen Maw. The second item I have no clue which one it is.

You can purchase Gatecrashers in Queen's Berth.

Sorry, no answer here but I am also looking how and where to obtain it. I have completed the game with almost all the unique weapons, but for this one I have no clues where one could potentially receive it (hopefully not on one of those plagued ships, I ignored most of them until I received once unique gloves).

You mean it depends on the ending in pillars of eternity 1 the white march if the armour is sold or not? I did not import a savegame from PoE 1 but generated one in Deadfire where I picked she killed Harmke. Never found the breastplate in my playthrough. As feliznav said, it is most certain you have to let her spare the guy so that she gets hammered by the villagers (and eventually ends up as a breastplate in Periki's Overlook).

I have both, but unfortunately do not remember exactly much where I got them: I know the belt I had it in my stash for a long time, perhaps it was obtained just by questing in Neketaka. Blightheart is rather uneventful how it is obtained: you loot it from a Wrecked Ship (or similar) on an souther island, if I am not mistaken in the middle. Sorry for not being able to provide more specific coordinates!