You can find the latest raw chapters of Black Gakkou ni Tsutomete Shimatta Sensei (I Messed Up by Teaching at a Black Gyaru School!) on manga hosting sites, though some scanlation teams have previously dropped the series. Raw chapters are often available on platforms like WeLoveManga, with updates sometimes appearing on MangaDex.
While user-uploaded raws are common, official Japanese chapters are published through Kodansha and can be found on services like BookWalker. Note that some unofficial versions may have different censorship levels compared to the official tankoubon releases. You can find the latest raw chapters of