>>I have plenty who hide emotions and/or injuries, but I'm not sure they're rigid enough.<<

Well, does the 'shell' have to be rigid and unemotive? Because there are plenty of people who suppress stuff, while outwardly appearing to be happy, healthy, calm, etc. Sometimes it could be displacement, but other times it is an emotional version of protective camouflage.

If looking for people with emotion-shells...look for caretakers who hide their needs, angry people covering up sorrow or an emotional void, and people who are expected to be happy. Also, see toxic positivity.