Reliable Royalty - Galdin Quay
First Available: Chapter 3
Other Requirements: Complete A Stone-Studded Stunner
Location: Galdin Quay
Rewards: 1,500 EXP & 1 Sapphire Bracelet
This quest can be started by speaking to Dino after you complete the A Stone-Studded Stunner quest. The Van, Interrupted quest that you get from Lestallum is also completed in the same area as Reliable Royalty, I recommend you do both of these at the same time.
You can find the Sapphire Stone in the northern portion of the quest area. There is a spot by the river where you'll battle a pack of Sahagin enemies and tucked away in a little alcove in that area you'll find a large mound, inspect that for the Sapphire Stone. A picture of this mound is shown below, if you're still having trouble locating it.
Completing this quest will unlock the No Pain, No Gem quest which is the second to last quest in the chain from Dino.