This guide will let you know how to get more gifts or where to buy gifts in Fire Emblem Engage.
You will find the Pretty Pebbles, Spirit Gem, and Horse Manure at the start of the game. These are the only gifts you can get until chapter 14. So you have to follow the story for chapter 14 and then come back to the Somniel map. You will get a notification that the flea market has been found. So make your way to the flea market speak and buy the gifts from there.