A simple way to get this is to get a MG vehicle of some type and park it right in front of the Villa entrance. Climb in the gunner seat and destroy the trees/shrubs etc that you can. Enter and exit the villa and the ammo will be reset along with the items. Just repeat. You do not have to have the coop partner in the car they can just be idle where they spawn. I had another PS3 and alt account as my partner and just used my main to shoot all the stuff until it popped up.