One large ASF is fine for an adult ball python. I only feed my very largest females (all over 2000g) a single large ASF a week, my large ASF's are usually between 100-130g. An adult bp doesn't need anything more than 100-150g of food a week to maintain a healthy weight. I believe there are several other people on this forum who will tell you the same thing.
Good luck, I hope you can find a food source that will work out for you.