Apologies for the delay in responding to this topic - were you able to find a solution in time for your biennial election?
Interesting. There is a filter in the review queue to filter by topics and posts that have been deleted, but not to filter by hidden. I also checked the staff action log and there is no option there to filter by e.g. “post hidden” either.
So yes your best bet is a data explorer query. I had a quick search here but did not find one so if you need this you’d have to create it. Since you are a hosted customer you could reach out to team@discourse.org to ask for help.