I don't think anyone has created a resource that easily shows exactly what you are looking for - so you're probably going to have to do your own research manually.

If you haven't found it yet, this github project tracks tracks most known lemmy instances and tracks some high level metrics for them. Pay attention to the "BI" (Blocked Instances) column which shows how many instances they are blocking as well as the "BB" (Blocked By) column which shows how many other instances block them. It's worth pointing out that the "Users" column represents active monthly users and not total users.

https://github.com/maltfield/awesome-lemmy-instances