Is someone that is both more knowledgable and responsible than me going to update this page with HP locations?
I know there are a few spots on certain maps where they have spawned randomly. I've found them in caves near Ember Caves, Ishtar, Venus, on more than one occassion, but it's not a consistent thing.
As with the normal pikes, heavy pikes will stay with you until you leave the area completely, they do not de-mat like the sparrows do. I've even handed the pike off to another player, they're semi-perm on the map, until destroyed.