Not too hard to find. Park below the kirk at St Martins and take the left of the three tracks ahead of you. About quarter of a mile in you pass the gate to the Abbey on the right, then another field gate on the right. About a hundred yards past this on the left a gently sloping track leads down to an old stone bridge. Cross and follow the path up to the left, then cross to the fence and follow it to the right. After a couple of right hand turns following this you'll see a wee clearing - and there's the circle.
Pretty disrupted, about 6 stones of a possible ten left, and all recumbent. Nice atmosphere though, and there's a bonus - a cup marked rock about 50 feet SW of the circle.