Quite easy to find although it is not visible from the main road.
When you arrive in Shap, park near the Kings Arms pub. Between the pub and the house next door is a public footpath sign. Follow this sign although it looks like you are walking up someone's garden. Over the stone stile and follow the path to the right. The footpath takes you straight past the stone.
The stone was much bigger than I expected – approximately 1 metre high by 2 metres square. For some reason I really liked this stone and would recommend a look when visiting the other sites around Shap.