So, the Atropos torpedo racks seem to be hands down the hardest weapon to obtain in the game.
I'd like to put them on my modded Gryphon (unlimited missile autoforge on a 3 minute cooldown), which honestly is the only sensible situation to use them... but I'm clueless as to where you can get them.
From what I see, the only ship variants in the game that use Atropos racks are Strike Hyperion and Strike Aurora - both are extremely rare ships to begin with, but to encounter them in those variants seems to be an achievement, as I don't recall ever seeing those. As for Remnants, those drop Atropes, but only single launchers, not racks.
Buying them is out of question too. Things are complicated by the fact that I'm on a no-commision playthrough, but it seems commisions don't help much either, as these weapons don't pop in any military market consistently either. I think I once saw them on a Persean League military market, but I'm not sure (and it doesn't make sense really - they don't use that tech). Not even Tri-Tach militaries seem to have them on sale!