There is a special spawn place for Sammies in Lake Foscari.
You can go to that location by passing through the big labyrinth at the far right side of the map.
When you reach the area and see the forest at right, just go a little deep in the forest so you don't really have to deal any other creatures other than sammies and chest-creatures.
I stood at a place like this and there were nearly no other creatures reaching me. So you'll be able to loot Sammies easily till 25th minute.
They won't spawn if you are not using a Tides of Foscari DLC character.