There are some reseeding petunias. Some reseed better than others. The best I've ever grown were Laura Bush petunias. (Seeds from Wildseed Farms). They reseeded like crazy, for years! I first wintersowed them. They were very popular on GardenWeb's wintersowing forum some years ago. Here are some volunteers in my yard in 2009.
https://www.wildseedfarms.com/...
Karen