For the max damage jewels (+30) you can get them from Uwe, Heidi, or Treemugger in Karamelle. Or if you're like me and are too lazy to farm the best, you can the +27 ones in Karamelle City (near the dock).
Also what do you mean by other stuff? If you mean other jewels, here are some.
For pierce jewels, my favourite place to farm them is from Bumbai Rebel Warriors in Yakhal Mountain, Mirage. They drop all school pierce jewels, decent drop rate, has around 2k health, Fire school so no Death resist, and does not have any shields or negative charms. Scarecrow+Epic kills (no critical) with at least 130 outgoing damage.
For pip jewels, the Death Ghultures in Caravan, Mirage drop them (as well as Couch Potatoes). They have 30 Death resist and do know Dark Pact, so if you farmed the pierce jewels you can just hit through. Scarecrow+Epic with a sharpened blade kills (no critical) with at least 134 outgoing damage, even with no pierce.
Everything else its best to farm Heidi in Gutenstadt, Karamelle as she drops all of them and has a cheat that buffs you. But she may not drop the highest health jewel. You might need to farm Abberant Paradox or Uwe for that.
