Question about farming Kepler weapons

Now that I am starting to have T2/T3 weapons drop, I went back into Kepler to start farming the new DLC weapons. I ran a campaign mission of Fabled for the first time and.....no weapons. Do they just not drop from campaign mission once you've completed the legendary campaign? What's the most efficient/fastest way to farm these? I'm REEEEEEEEALLY hoping I dont have to just go play the sieve until my ears bleed. Apologies if this has already been discussed. Didn't see anything recent.