Some local comic book stores or libraries could have it. You can also check dedicated manga websites. Sometimes, you can find it on eBay or other second-hand marketplaces too.
You might try looking on popular online comic platforms like Comixology or Amazon Kindle. They often have a wide range of manga available, including Oldboy in English.
The best place to start your search for Oldboy manga in English is on well-known manga subscription services. For instance, Crunchyroll Manga or Viz Media's online store. They usually have a good collection and might have what you're looking for.
Chapter 457, ""Back Against the Wall", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 83, "Can Actually Carve Flowers?!", is the clearest early answer because it turns Flowers's situation into a concrete plot event. The chapter turns that into something concrete by moving from When they received the task, the three of them were already...
Chapter 444, "Wait and See", is the clearest early answer because it turns Dean Yu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Carrying a backpack, Yu Li walked for over ten minutes but ultimately...
Chapter 190, "Aren't We Friends?", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. Early on, Several people who didn't understand fell silent.. By the end, Because he saw the pack of cigarettes pinched between Jiang Li's....
Chapter 627, "Definitely Not an Accident", is the clearest early answer because it turns Don's situation into a concrete plot event. The chapter gives readers a real answer by opening on He looked at the sinister smile lingering in Jiang Li's eyes, then at...
Chapter 189, "Do You Still Like the Gifts from the Program Team?", is the clearest early answer because it turns Like's situation into a concrete plot event. The chapter gives readers a real answer by opening on Seeing his painstakingly planted roses trashed like this, even as a...
Chapter 228, "Younger Brother is the Number One Hater?!", is the clearest early answer because it turns Mr's situation into a concrete plot event. Early on, Huo Ziyang had not stepped out of the house for a whole week..
Chapter 456, "It's Not Too Much to Ask for a Game Console, Right?", is the clearest early answer because it turns Yu Li's situation into a concrete plot event.
Chapter 238, "The Guests Were Dumbfounded, The Audience Was Excited", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Li was actually first on all three leaderboards?!
Chapter 188, "First in Grade, It Can Only Be Me, Jiang Cheng", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event. A useful checkpoint is the way the scene starts with With a "snap," the pencil Jiang Cheng was using to draw broke on the...