To promote the Pokémon GO Tour: Unova, three codes have been announced to give players Timed Research to encounter Tornadus, Thundurus and Landorus. Players need to catch 156 Pokémon originally discovered in the Unova region in the Timed Research in order to get an encounter.

Codes:

Incarnate Forme Thundurus: 4Q4UZLY6MUH9K
Incarnate Forme Tornadus: 4RD3GGA4ZMEGP
Incarnate Forme Landorus: 9PTA874LYDAJH

Source: https://x.com/PokemonGoApp/status/1894537937183764600