Where can I find datasets for the task of chord recognition (machine learning)?

Question

Sound processing

I study methods for analyzing musical works and identifying chord sequences.
Actually, the main question is, where can I find (preferably free) ready-made MARKED data on which you can train and test? Perhaps someone was engaged in a similar task and knows the sources.
Also, if you prepared the data yourself, please leave a couple of your tips.
At the moment, I have found only:
1. Works by Bach
2. on the MIREX website ( www.music-ir.org/mirex/wiki/2015:Audio_Chord_Estim... there are 2 datasets, the second without audio (which, as I am told, is bad , because cutting an audio file into such small parts is very difficult (and cutting in general))
I also did not find audio for the first
one.Thanks.