The best way to farm accessories is to literally farm accessories hhhh

Soon the AQ7 will come and that will introduce Devil accessories which are fucking insanely good depending on effects.
They introduce evasion, crit rate and uh... something else?, that are rare to find on accessories.

They also sometimes have bonus effects that doubles effects
e.g. base ATK on normal is 2% (3% at lvl 50)
base 3% for ancient (4% at lvl 50)

for Devil, it's 4% base (5% at lvl 50) BUT there can also be a bonus that makes the base 8% (10% at lvl 50)
you can get that for healing, atk, def and HP

...but the ancient/devil bonus isn't always guaranteed, obviously, since for example you can still get a base ATK of 2% on a devil or ancient accessory as if it were normal.

IMO, the AQ7 are actually pretty easy, despite having super low affliction rate... you HAVE to use an ability every turn otherwise 3/3 boss does oversized DMG to all allies (3-6K) depending on which element you use.

6/7 are the best, though as they do drop a guaranteed 2 SSR each...