The official Pokémon movie website has updated. Translations follow:
Media Information
Magazines:
Saturday June 1st: "CINEMA SQUARE" - Merchandise giveaway
Thursday June 6th: "Monthly Shonen Magazine" - Merchandise giveaway
*Note that these are the scheduled publication dates, and as such are subject to change without notice.
Source:
https://www.pokemon-movie.jp/news/?p=3649