Where to find Landorus in Sun, Moon, Ultra Sun & Ultra Moon

Only in Ultra Sun & Ultra Moon
Static Encounter: Ultra Space Wilds, Ultra Space (With Tornadus and Thundurus)

Guide: Ultra Space Wilds: Every Legendary in Ultra Sun & Moon

Landorus also appears in

How to get Landorus in Sun, Moon, Ultra Sun & Ultra Moon

Its base catch rate is 3 out of 255 (higher is easier); the catch rate calculator works out your odds with each ball.

Landorus in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)