Buying a firearm out of state without adhereing to the laws of your local state is illegal. Obviously people still do it.

Obviously that's the case, so what's your proposal to fix that?

If they don't have it on record and they're owned illegally the police won't know if there are firearms anyways unless they search an entire house. It's unlikely a judge will sign a search warrant for a private residence just because someone has a mental health issue. If they do and they're found that's a method to remove them from unstable people, and also a felony if they were illegally obtained.

A map of sexual offenders is completely different than a map of firearms owners. One is from an illegal activity and the other is from a perfectly legal thing. It's also a map that can be used by criminals to target certain residents to steal firearms. Nobody needs to know if I own a gun or not it's not their business.

There already is a way to confiscate firearms from unstable people. Connecticut has red flag laws.

I second this area. There's miles of mountain biking trails off the main body in the state forest as well.