I don't know how they're finding it (and why this post specifically), but I posted this nearly two years ago now, and it's still getting answers fairly regularly.
While trying to figure out how Vietnamese students are preparing for the HSK7-9, I stumbled upon the textbook Capstone Chinese 《顶石中文 高级汉语综合教程》. Despite not having HSK in the title, it says in the preface that it's designed for the HSK7-9.
It was published in 2023, but I didn't realize it existed until recently (otherwise I would have studied it already). I bought a copy, and posted about it in more detail on Chinese-Forums. I'll probably use it for my own HSK7-9 prep.
It uses the 3.0[2021] HSK7-9 syllabus. It doesn't cover every HSK7-9 word (as there is 5000+ of them), but it covers a range of topics relevant for the HSK7-9.
I didn't feel like studying, so I made some chengyu riddles:
The chengyus are relatively common. They're all 4-character chengyu where I represent the characters with emojis in some way. Enjoy.
Edit: Well done, you got them all. Here's the anticipated answers:
>!叶公好龙 独一无二 一丝不苟 画龙点睛 对牛弹琴 杯水车薪 一针见血 小心翼翼 见钱眼开 鸦雀无声!<