Hi JE L,
You can visit Shin Okubo located on the JR Yamanote Line in Shinjuku.
Shin-Okubo, also known as Korea Town, is a safe haven for K-Pop and K-merchandise. As such, most of Shin-Okubo revolves around mostly selling boy band paraphernalia. However, there are other items one can shop for in the small section of Tokyo. Cosme shops feature Korean products for ladies’ and men's’ skincare, and even Korean food.
When it comes to K-Pop shops here are four stores that are recommended;
IDOLPark is a cute little store and café combo right outside the station. The shop is tiny and sells tiny K-Pop charms, keychains, postcards, and so on. The shop doesn’t have much in terms of variety, but their cheap CDs are great. If you keep walking down the street you’ll find more decked out stores, but IDOLPark also has a wonderful café upstairs that serves coffee and ice cream. If you only want to do a little shopping and a snack, it’s perfect.
2. Star Shop
Right across the street from IDOLPark is the Star Shop. It has two floors devoted to posters and calendars and actually has a wide variety of Korean actors as well as K-pop stars. It also has a vast array of clocks and coffee mugs with idols' faces on them. There are Korean snacks on the first floor in bulk, as well, so if you want a small taste of Korea I suggest heading over that way.
3. K*Star Plus
K*Star Plus, which is one of the better shops. It has three floors with a lot of variety. The first floor is devoted to CDs and DVDs. Name a K-Pop band and they’ve got them. They also sell Korean soundtracks to K-Dramas and K-Movies. Their second floor with band special collector jewelry that most shops didn’t have. The band names and people associated with them are beside the glass so you can find your favorite singer’s jewelry. So far as I could tell, this shop is the only one to have band hoodies, so if you’re looking for one head straight there.
4. The Plaza
The Plaza has CDs and DVDs, but it had the best Blu-ray collection out of all of the shops. It’s also got the widest selection of Korean snacks in bulk. Along with the keychains, posters, and mugs, you could even find band t-shirts along one wall in the back. I believe they’re one of the few stores to have t-shirts in the first place and definitely have the best selection. However, the prices for everything were a bit more expensive on average than the other stores I listed before.
You can visit this link https://taiken.co/single/shin-okubo-shopping-guide/ for Shin-Okubo Shopping Guide.