Though there are many makers of similar soft drinks, traditionally (since 1956) the most reknown maker is Tassoni.
The company has been recently sold (2021) and the buyer, Lunelli group (more famous for wines) has promised (but seemingly hasn't done anything about it till now) a new international expansion.
It is recent news that they are re-positioning the brand toward luxury beverages, JFYI (Italian):
https://www.repubblica.it/il-gusto/2023/03/24/news/cedrata_t...
The cedrata is made with Citrus Medica or Citrus Diamante. This is basically a larger and sweeter (less acid) lemon.
The chinotto is made with Citrus Mirtyfolia. This is basically a small, bitter orange.
If this keeps up, I'm going to become an italian soda smuggler.
What you can do (at home) is to make it yourself, there are good chinotto syrups and you just add sparkling water to make a chinotto that is better than the pre-made soft-drinks.