Gun restrictions would make no difference, a guy in Japan made a gun from wood to do what he did to Shinzo. The problem is intent.
Also regulations never end, if you want to see how far this goes look at the UK. You are not allowed to use pepper spray or a tazer, you can be arrested for using a knife to defend yourself from an intruder and get more jail time than they did.
The problem with trying to regulate things like this is it never ends, the people pushing for more controls don't just get to a point they are happy. They keep pushing more and more for carbear land, this is why you can never give an inch. Cause it will never be that inch, and instead is the thin edge of the wedge.
https://www.videogameschronicle.com/news/uk-man-jailed-for-four-months-for-carrying-6-inch-zelda-master-sword-in-public/