Try the Dressmaker's in Calis. She makes and alters clothing so I am sure she could make up some cushion covers and she is really reasonable priced for the work she does. I have used her a number of times and have always been pleased.
Walking up from the prom on the Main Street, turn right at the lights and walk along the road, there you will see mannequins outside with dresses on them, just go down the flight of stair to the shop.