The interesting thing about googling “self defense certification” is that many of the courses are online. This doesn’t seem particularly useful, in my opinion. As you know as a martial artist, hands-on practice for most techniques is critical because you have to have the muscle memory and practice touching people a variety of heights and sizes to figure out where pressure points are and how to hold, push, twist, etc. I have a black belt in taekwondo, which included lessons in self defense and one-step sparring at each belt level, so I have experience in self defense but would not consider myself qualified to teach it.
This particular thread was posted a few years ago. It appears that at least one of the respondents does live training for self defense instructors.