I came across one a while ago but it seems to be run by some folks that I don't think I could trust or even mention in any professional contexts. :/
I was kinda hoping #FediDB would be tracking something like this but I didn't see anything in their api
@mauve right, while I agree it would be useful, this kind of thing doesn't exist for a few reasons. one, as you found, bad instances like to track who have blocked them, either as a kind of high score or for retaliation. two, collecting such statistics would require instances to disclose their block lists in a machine-readable format, which plenty do not do and are not willing to do.