Q191
Are there any spells/effects that can actually pierce a Mind Blank Spell? I don't mean Dispelling it, I mean seeing through it.
See through it how exactly? You mean they've made themselves magically immune to detection and they're using the divination-immunity clause of Mind Blank to prevent them from being found?
An antimagic field would make them immediately apparent, of course. And you might be able to somehow heavily metamagic Faerie Fire such that it applied to everyone in a large area rather than needing to be specifically targeted, in which case it would work fine.
The DC 40 application of Spot to pinpoint an active invisible creature making no attempt to hide would work if it's just Mind Blank+Invisibility, since it's just an Extraordinary thing, not any kind of divination magic functioning directly on them. And DC 40 is easily doable at the kind of levels Mind Blank is being tossed around.
If the network of spells that hides them is more complicated than that, you'd need to make the DC 80 Spot check to automatically ignore any illusion. Which is still doable but you'd need to devote substantial build resources to it.
Beyond that...epic magic?