I can't seem to find sleeves for guardians/heralds/institutions. Do anyone else have any better luck? I've sleeved everything else (all expansions) and it would be a shame to not "fix" these as well, don't you think?

There are some. IIRC, Tromdial got those. Maybe it's easier if you PM him, asking. Sorry, I couldn't help you, since I laminated all Investigators / etc.

I think you have some answers over at BGG…