One of those problems who only exist on the place where you can buy a Assault rifle on the same store where you buy milk, eggs and a frying pan

I'm guessing this was copy pasted from a translator. It didn't get it right. This is how it should read:

One of those problems that only exists in a place where you can buy an assault rifle at the same store where you buy milk, eggs and a frying pan.

Also, you can't buy assault rifles at Walmart. The rural stores carry hunting rifles. I live in a suburb and the one near me doesn't even sell ammo.