I love the Poison Arrows and recently started using the Poison Throwing Knives.
So, I always keep an eye out and mark on the Map my best spots to gether the OS.
Along the river on the opposite side from Saint Denis. Road and fenceline from Caliga Hall there. Usually the side closet to the Horse/Carriage bridge [[would be on the Left facing the water. Also on the other side of the trees that run along there-just past bthose where SD is on the left along with the pennisula usually having three Gaters resting.
The area where you hunt the Legendary Boar. Look around clumpps of dead trees between the RR tacks and the trail.
Behind Shady Belle. I can usually only access it safely after the mission with Lenny to clear it out. If you face the water with the shack and dock on your right that general area.
All three locations seem to vary slightly between Xbox and PS4 but hey are usua;ly there.