The official Pokémon website has announced that starting on March 5th, 2021, select retailers will begin selling the Pokémon TCG: Sword & Shield—Battle Styles Build & Battle Box earlier than the expansions release date on March 19th, 2021.

Get the Pokémon TCG: Sword & Shield—Battle Styles Build & Battle Box Early

Select retailers will offer this Prerelease set ahead of the new expansion’s release date.

The upcoming Pokémon Trading Card Game expansion, Sword & Shield—Battle Styles, will be released on March 19, 2021, but you can get some of these new cards early at your local hobby store. Starting March 5, 2021, select retailers will be selling the Pokémon TCG: Sword & Shield—Battle Styles Build & Battle Box, giving fans the opportunity to check out the expansion before its release date and build a playable deck in the fast-paced Prerelease format.

This format lets players construct and compete with a 40-card deck with four Prize cards set aside at the start of play. It's a great way to get in some quick games with family or friends and begin developing strategies ahead of the expansion's release. Each Build & Battle Box includes a 23-card Evolution pack featuring key cards from current and prior sets, including one of four unique foil promo cards. You also get four Pokémon TCG: Sword & Shield—Battle Styles booster packs and a deck-building tip sheet.

Source: https://www.pokemon.com/us/pokemon-news/get-the-pokemon-tcg-sword-shield-battle-styles-build-battle-box-early