I’d start with Chicago in Harajuku for the yukata, or Fukufuku in Shinjuku since it’s close to you. Secondhand samue is harder to find; I couldn’t confirm a shop currently stocking it.

- Chicago in Harajuku is a good option for secondhand yukata and obi. Budget roughly ¥2,000 to ¥5,000 for the garment, though stock and prices vary. It’s a short ride from Shinjuku on the JR Yamanote Line. Check the [official branch list](https://www.chicago.co.jp/store.html); [recent shopper reports](https://www.reddit.com/r/Thrift/comments/1jpfodn) give that price range.
- Fukufuku (福服) is a specialist secondhand kimono shop at Shinjuku 2-7-2, open 11am to 7pm. It’s convenient to try first and ask about both items, though I haven’t confirmed its current yukata or samue stock. [Official shop information](https://shopping.geocities.jp/fukufukukimono/).
- Miyoshiya (三喜屋), in Nakano Broadway B1, is another affordable secondhand kimono shop worth browsing for yukata. It’s about five minutes’ walk from Nakano Station, an easy trip from Shinjuku. Prices and selection vary. [Location and reviews](https://map.yahoo.co.jp/v3/place/JUJHJidzrOI).

If you’re happy to buy new samue, Kohtariya in Asakusa currently advertises an in-store cash special of ¥4,800 including tax. The shop is at Asakusa 7-2-7. Check availability before making the trip. [Official store page](https://www.kohtariya.com/tenpo/tenpo-tokyo.htm).

You can show staff 「中古の作務衣と浴衣を探しています」 (“I’m looking for secondhand samue and yukata”). Try them on and check for stains. For the yukata, ask whether the price includes an obi.