It occurred to me that I don't think my retainers have ever brought back Darklight gear pieces, which has set me thinking and realising the gear series is in an odd place overall.
My understanding – though it was before my time here so I'm not certain – is that it was the first tome gear set for ARR (equivalent to the Yasha/Ronkan/Moonward sets) but being very early days before the current pattern of gear handling was established, they moved it into being dungeon gear on top of the sets that were already there.
Previously when I've been trying to acquire Darklight pieces, reference sites indicated that there was a specific sub-set of each gear type in each of the three dungeons, so you could narrow down the right dungeon for what you wanted, but it seems that this has been rearranged and it's now just everything in every chest, creating a very low chance of getting the piece you are after (whether you're looking for Darklight or the other sets), compounded by the fact that chests aren't even guaranteed to hold gear pieces and may only yield accessories.
Combined with the lack of a guaranteed piece at the end of level 50 dungeons, it means some quite cool pieces are locked away and barely seen. (The mage outfits in particular have never been reused, even when the other sets were reused as PVP models.) All three sources are optional dungeons.
So this has all been a long ramble around the question: could something be done about this to make them more easily available?
If they're not currently in the retainers' loot table, they should be, just like all the other dungeon gear and tome gear.
And more ideally, they could get shifted out of the dungeon loot entirely and be added back to one of the other endgame vendor sections. Perhaps tradable for antique tokens, like you currently can for the i90 "vintage" job sets, or add it to the allied seal vendors like the i110 sets.
Allied seals seem like the most equivalent option to the expansion counterpart series, which shift to being bought with hunt currency once they are no longer bought with endgame tomes.