I think the true soap nuts are tropical trees, though according to Wikipedia there are some that grow in the US south and may be worth you checking out:
https://en.m.wikipedia.org/wiki/Sapindus
For those in cooler areas horse chestnuts (Aesculus hippocastanum, not the edible Castanea) are related to soap nuts, work just as well, and will grow in temperate to cool areas. The non-edible nuts crushed and dried are the parts that are used for saponins with horse chestnuts.