Last I checked, LibriVox had about 11 hours of Mandarin audiobooks and Common Voice has 234 validated hours of "Chinese (China)" (probably corresponding to Mandarin as spoken on the mainland paired with text in Simplified characters, but who knows) and 77 validated hours of "Chinese (Taiwan)" (probably Taiwanese Mandarin paired with Traditional characters).
Not sure whether that's enough data for you. (If you need paired text for the LibriVox audiobooks, I can provide you with versions where I "fixed" the original text to match the audiobook content e.g. when someone skipped a line.)
