I'm at HSK3 level and struggle to find things to read outside of my actual textbooks with precisely-calibrated texts. If I can't read am average billboard, what should I read to improve?

I'm at a similar level, maybe a little behind that. I don't have any advice for you, but I'll relate the path I am planning to take. Would be happy to hear others' thoughts, too.

My feeling is this level is just too early to read "real" texts, so I am continuing to just use graded readers. I use the Du Chinese app for this, it contains a bunch of short stories at different comprehension levels, and has a spoken accompaniment to each story read by a real speaker (not AI/TTS). I also have some physical books from LingLing Mandarin, I like the challenge of not having a dictionary immediately to hand like I do in the app. My hope is by the time I finish with the Advanced stages of each of these sets of readers, I will be able to start reading "real" texts and fill in gaps with a dictionary app, at which point there is an infinite supply of material.

I do worry I'll end up at the "10% missing comprehension" described in the article, though, at which point I guess I'll try to find even higher level graded readers, if they exist. We'll see.

1. Take a large collection of text, e.g. from https://opus.nlpl.eu/corpora-search/zh-CN&en

2. Split into sentences and tokenize sentences into words, e.g. using https://github.com/fxsjy/jieba

3. Count how often each word appears and sort sentences by descending frequency of the least common word.

4. Use binary search to find a location in the sorted collection of sentences where the difficulty feels about right.

Of course this gives you a collection of disjointed sentences, but you can always go to the original file and look at the surrounding context when you find an interesting or confusing one.

It is normal that there's no native content at HSK3 level. It would be like looking for native content at A1 level in English. But I found the "actual textbooks with precisely-calibrated texts" / graded readers are not that bad. My teacher is a martian was OK, I want to read The Monkey’s Paw now.

Read simple novels and look things up in a dictionary when you see a bunch of words that don't make sense. Watch shows with subtitles and do the same. Chat with people in the language. This is how non-natives learn English outside of school. It's also how non-natives learn Chinese.

Ain't nobody downloading stuff from GitHub and splitting things into tokens to learn English like the other commenter is suggesting lmfao. But people are obsessed with bizarre and completely inhuman methods like that when they learn Asian languages. I cannot understand why, and it's seriously just Asian languages.