In Minecraft Legends, Lapis Lazuli is a critical resource for spawning a majority of the allied mobs. Unlike most of the other resources such as wood, stone, and iron, it is not mineable from blocks in the world. Here are the only known avenues for accumulating Lapis in Minecraft Legends.
Piglins
While demolishing Piglin structures causes Prismarine to drop, killing Piglins themselves drops Lapis. Raiding bases and losing troops in the bargain can lead to diminishing returns on Lapis farming, so it is recommended that you pursue smaller Outposts, Piglin Patrols, and defeat Piglin raids on villages and the homesteads of allied mobs. The latter has the additional effect of spawning a replenishing chest that accumulates Lapis slowly over time, as well as other random resources, and that is located near the fountain after rescuing the village.
Chests
While not as reliable a source as Piglin-slaying, Chests carry a good chance of dropping Lapis as a reward when opened. These can be stumbled upon throughout the world, in addition to the aforementioned Village fountain Chests. There is an element of randomness to non-village chests however, as anything and everything but Lapis could also drop, including Allays and Gold among others.
Tip: Construct the Improvement: Shared Village Chests. It will pool the resources accumulated in all liberated village chests across the world map, allowing you to visit just one in order to collect them all.
Lapis Flag
In PvP multiplayer, a structure called the Lapis Flag can be found under Player Building Melodies, and can be constructed to enhance the slow and steady drip of Lapis to the entire team. Each flag itself costs 25 Lapis, 100 Prismarine, and 300 Stone, and as many flags as needed can be constructed. They are also destructible, so be sure to defend them from attack, especially given the resources that have to be poured into their construction.
As resources go, Lapis Lazuli is one of the easiest to farm, once you get a good rhythm going, so farm away!