Searching for "GDZ" (готовые домашние задания / prepared homework answers) for Russian language textbook typically yields results for two main editions widely used in vocational schools (SPO) and senior high school classes:
Sites like Znayka or Gdz-putina occasionally host user-uploaded solutions for specific editions. gdz po russkomu jazyku dudnikov
You can often find the full textbook (with answer keys in the back for some editions) on Twirpx or similar educational repositories. Standard Content Structure gdz po russkomu jazyku dudnikov