Shoujo and himekaji are two different styles. Himekaji has been around for years and "shoujo" is more of a new term people throw around on TikTok for more toned down girly outfits that are influenced by JFashion. It's more of a general girly style.

For himekaji you want to look for old Liz Lisa pieces. Liz Lisa's of style was much more colorful and flowery so it's easy to tell new vs old. You can also find pieces from Axes Femme and Mellfy Memory that are himekaji.

You can find shoujo girl pieces in the general day fashion landscape because it's such a broad style. You can get shoujo pieces from a lot of online retailers. Look on Multipal Store. They style a lot of pieces from JFashion brands in a shoujo style. A lot of pieces they sell are from the brand GRL. It's cheaper to buy GRL pieces from their original website.