Are there any mindless creatures that have vulnerability to mind-affecting effects?
Oh, and I don't just mean that they lose the mindless trait, I mean specifically having no intelligence but having a specific vulnerability towards mind-affecting effects
Not that I know of. Generally speaking having the mindless quality specifically makes you immune to mind affecting. That's literally all it does.
As an example:
Mindless: No Intelligence score, and immunity to all mind-affecting effects (charms, compulsions, phantasms, patterns, and morale effects). An ooze with an Intelligence score loses this trait.
I don't think it's possible to have the mindless quality and be vulnerable to mind affecting effects.