Legendary distributions for 2018 (February-November). Looks like each month except July you get a different one based on whether you're playing (Ultra) Sun or (Ultra) Moon.All Level 60 or higher, and if February is any indication for the rest of the year, it looks like the Ultra games will get "ultra" versions of the Pokémon at Lvl. 100.
"The problem with certain shy timid girls is you can't just take them to a bar and f***'m. You gotta put up their Christmas lights first." ~ jukester