What we did - we set up an email account just for college. My daughters first name, HS name, grad year @ gmail. so like susansmithtown21@gmail…example…not her email 
Then we started with a list of 100 schools - I know most don’t do that - but we looked at every school in the country and that was our beginning list.
We got all on their info requests - so they started emailing. I managed her account. I’d open emails, etc.
I think when you interact with their stuff - the schools that will - will send. I think 6 of the 21 we had gave a fee waiver - and then as you said, schools you never asked about - like Ohio U did too.
Pitt had one after an info session, Miami Ohio after we took a tour.
Then there’s already a ton of schools that have no app fees - you can find them by googling niche colleges no app fee.
The crushing blow is sending the ACT but more and more schools are letting you self report.
Good luck.