David Reinhart wrote:

It's my understanding that ejection seats aren't allowed on civil aircraft
because the pyrotechnics used are illegal for civillians to own. They're
considered controlled military munitions.

It's possible for private citizens to obtain permits to own military munitions.
They're classed as "destructive devices" and controlled by BATF.

George Patterson
This marriage is off to a shaky start. The groom just asked the band to
play "Your cheatin' heart", and the bride just requested "Don't come home
a'drinkin' with lovin' on your mind".