Look for Children's Toys on the right. Also, regularly ping your department heads, I believe I have seen the repeatable pop up there once.
The DOFFS spreadsheet is community-authored, so if you don't see a mission, it might not have been found yet.
Also, the mission is fairly rare, and it has a three-day cooldown after you complete it. (Ie, you can't get another artifact for three days). You can purchase the artifacts on the exchange if so inclined.
As I said, I regularly check my interior and do DOFF missions all the time. Guess I'm not lucky enough to see that rare mission to get the artifiact.
And to heck I'll buy them off the exchange, those prices are greatly over inflated.
Heretic should revise the mission in some way, perhaps have pieces part of dropped off normal mobs and you assemble it via crafting.
I just noticed someone else in another thread mention that they do their doffing at ESD, and that made me want to make sure you are checking for the "Negotiate Delivery of Rare Commodities" mission in Cardassian space. . .
As I said, I go doffing and very frequently go thoughout all STO space, especially cardassian space on 6 characters. And I go inside my ship in doing missions too, check department heads as I travel. And I've yet to see this mission.
Heck, there are even rarer missions like the Kobyoashi Maru that others gotten on the first week of the revision. Something is not right. Unless Heretic is pulling a STF in where we hope to get tech and end up empty handed after months of play.
I saw this mission a couple of times over the weekend. So, it DOES pop. Heretic has said they are keeping the cooldown at 3 days for now until they assess the number of consoles coming into the game. I've got a stack of around 10 of them waiting to be 'made'. Just waiting for the right doffs. Hopefully, with the changes in the pipeline, I'll have enough 'resolve' doffs to start making them.
Just wandering about you're not too likely to find it on your own. It usually appears in only one sector, about 25% of the time from what I've seen. So if you aren't hitting every sector in Cardie space you might be missing it. As I said, check the spreadsheet, it lists where people have seen the mission: