A lot of these people get strong word of mouth referrals to their next roles. I’ve got a passing familiarity with the “Aerospace” SRE due to the satellite instrument and cubesat Linux ecosystem. And at least as far as I can tell, while there’s lots of people with the skills, not a lot of them would probably go around advertising themselves as SREs.

You’re best off looking at what each field has historically called it’s SR3 equivalent roles, like “chief engineer” or “lead engineer” for a lot of various aerospace engineering roles. These are the people expected to know everyone who knows anything they don’t and who are called in when the shit hits the fan.

In fact that’s a good way to boil it down, if you’re trying to find these SRE type people In other fields, “are you the person they call when shit hits the fan an no one else has answers?”

Hope the perspective helps!