From March 27th, 2020 until April 19th, 2020, the Pokémon Collecting Guide (ポケモンあつめようガイド), which is packed with tips for completing the Pokémon Zukan, will be distributed at participating stores in Japan including Geo, TSUTAYA, and Joshin. The guide comes with special Dynamax Crystal (ダイクリスタル) serial codes to allow players of Pocket Monsters Sword and Shield participate in a special Max Raid Battles against Stonjourner and Eiscue. The serial codes can be used until April 30th, 2020.

Source: https://www.pokemon.co.jp/info/2020/03/200319_gm02.html