Find them in dungeon chests
Find them in desert pyramid chests
Find them in bastion remnant chests
Find them in nether fortress chests
Find them in ancient city chests
Find them in woodland mansion chests
Find them in fishing loot
Trade with leatherworker villagers
Get them from chest loot in villages
Get them from chest loot in other generated structures
Kill ravagers during raids
Remove them from saddled mobs with shears in some versions/mods if supported