Potato flour is a very confusing product, because the same name is used for two different things:
"Real" potato flour is simply ground-up potatoes. Many recipes insist upon this type of potato flour, but the fact is that such a product does not exist! If it did, it would have a very short shelf-life, because potato is inherently unstable.
Potato starch is also known as potato starch flour and is usually sold as potato flour. All of the products below, and all of the potato flour products that we know of, are of this type.
It's worth noting that any bread recipe that calls for potato flour will work with the products below. We know because we have tried them!