See the KCAD DLC for Brush Info: including the Bonner Brush Pack and the Jason Nice Brush and Smudgy nice - the tools Susan keeps talking about! The list on that site will go over how to download and apply the brushes where to get them etc.
If you have issues with the download on that site: go to our course Google drive Folder here: SharedToolsBrushesEtc
As always - any questions or issues = Email your instructor
Below are a few links to available custom Photoshop brushes that are good for environments. (The majority are free brushes, but some are not.)
Downloadable Photoshop brushes by Kyle Webster. Free with Adobe CC subscription. The Concept Pack is good for environments.
DigitalBrushes.tumblr.com- An archive of tons of downloadable brushes. Some free, some not.
Environment Brushes by Dean Oyebo
Concept art brushes including brushes for environments by Evenant.