I've made my own. Measure the length then divide by a number that will make sense to you and use paper to cut one scallop to the length. Example 1: Your quilt is 52 inches long...divide by 10 to get 5 scallops 10 inches long. You can adjust the center-most scallop to fit the extra two inches from the example.
Example 2: Your quilt is 74 inches wide...divide by 7 to get 10 scallops 7 inches long and add a four inch point (or scallop) in the center to fill in the left over inches.