You can't see the church in the photo but it's behind the trees in the background, about a third of the photo in from the left.
It's not easy to get to!
Leave the churchyard through the gate in the corner with Bradbourne Hall on the right. Follow the path down through a wooded area and then over a stile into a field. Keep going downhill and about halfway down is a single gatepost on the right before a fenced-off scrubby wood - if you look on the OS map to the north of the church, the footpath goes to the left of this small wood with a pond in, which is actually an overgrown swamp! The stone is in the field to the right of the wood.
You can't see it from the path. It's easiest to see if you walk past the wood into the next field, then bear right and you can see the stone in another field to the right again.
But to actually get to it, I turned off the path at the single gatepost, and found a gap in the fence that side. There's a stream to leap whichever side you come from and the ground was very boggy despite the dry season we've had so it might be a bit of a challenge if you go when it's been wet.