Raw versions of the manga (untranslated Japanese pages) are typically available on Japanese digital storefronts or specific archive sites.
While raw sites are convenient for staying up to date with the Japanese release, consider supporting the series by purchasing physical or digital volumes. Weloma Download - Greasy Fork Raw versions of the manga (untranslated Japanese pages)
Reading Roppen Chapter 77 on Weloma Portable is easy. Here's a step-by-step guide: Raw versions of the manga (untranslated Japanese pages)