Need a trailer ball for my ATV

I went bumming around the yard earlier looking for a trailer hitch for my ATV, I want to snag my brother's ATV trailer that's out in the yard to move some stuff, but I can't get any of the four hitch balls off the trucks they're on. (Yes, I even checked the ones on trucks belonging to my brothers and nephews.)

I think I may end up buying one, but first I am going to try to get the one that had the best chance of loosening up off one of the trucks. It is mostly rust free, but rather than the bolt move, the whole ball spun when I tried to remove it. Need to find a chain wrench to hold the ball in place as I snag the trailer ball.