There is only one stone on Fyfield that has been recognised as cup marked.
http://www.users.myisp.co.uk/~gtour/Cup.htm
I know the farm stone you mean and think it may be the one Stukeley mentions;
"In a close on the left hand of the avenue, or east of it, not far from Abury town, is a pentagonal stone laid
flat on the ground, in the middle of which is a basin cut, always full of water, and never overflowing. The
country people have a great regard to it: it proceeds from a spring underneath and for ought I know, it may
have been here from the foundation of our temple."
I'm sure there are more cup marked stones around but unless it is found by a Pro Archaeologist it won't officialy be recongnised.
PeteG