Did you check with JoAnns on-line?? It's easier than driving to different stores.
If you can't find it, maybe you can make a medallion back with a very large
heart block in the center, a few borders and then a very wide border of your
backing fabric....
Also if you know the name or manufacturer of your fabric, the Fabric Search function on the FAB Shop Hop site is an excellent resource.
Good luck - Judy