There's a bunch of 4-star characters I'd love to upgrade to 5-star status... but while I've got all the COLORED shards I need for it, the requisite colorless 3-star shards, which are needed for ALL of them obviously, seem to be painfully rare. Sometimes I get a few from the Evo-Material Cache/Hoard, but since that has a 12-hour cooldown and they're far from guaranteed, you don't get too many that way. I've tried grinding various LoL X-level stages for them, but I mostly just get colored shards from that, and burn through all my hourglasses in the process.

Cosmos-stages don't seem to be particularly efficient at it - or maybe I've just been trying the wrong ones? Supposedly, any Battlefield-stage at Madness-level, and any Underworld-stage at Hard or Madness will do the trick, but again, I've rarely gotten any that way.

Am I missing something? Any good places for them, any good tricks to get them? Have I just been really unlucky? Or is it just a terrible grind to collect that particular component?