Where can I find the newly added sulfur in the game?

Sulfur can be found in grasslands and tundras, note that it will only be available on worlds that were generated after Update 11.1. If a dedicated server is used, WorldGenerator.eco also needs to have been updated from the template first.

You are of course correct, I confused the cold forest with the tundra.

I would not, your answers are literally always correct, haha.