I'm stating the obvious here, but that is a field modification. As you can see from Philly5G's post and in my experience, Piper delivered the airplane with straight control sticks.
I don't have an opinion on the modification but am simply clarifying that you won't find a Piper part number for a bent control stick.
From the photos, it looks as if those control sticks are longer than stock. If that is the case, they were probably bent aft for clearance from the aft tilt of the front seat.
My favorite rear seat control stick was in a J-3 I previously owned. It was cut down several inches and had an offset aft, not bent, the "offset" was reattached by welding. This allowed full aileron throw even when wearing winter gear which increased leg diameter by about 5 inches, it also provided excellent clearance with rear of front seat.
It felt very natural as the height was just right to allow my forearm to rest on my thigh. It was like that when I bought it, the previous owner had a 36" inseam like me. I suggest fabricating it, so it works best for you.