That supermarket thing...

So I saw the video of the attack and... another same thing as before. Military grade equipment available to be acquired from an 18 year old. My question is... Where to buy that stuff? At a certain point I don't ask why it happens, but where to acquire. I'm just curious of how easy and cheap must be to acquire that.
Hera a guy was planning to make an attack on a University and the things he was able to acquire was just some knifes, katanas and a crossbow, I think. What a noob.
"Go big or go home"