Step #7 in the I Heart Vanilla list
Stuporstar and Greatness7
Featured In Mod Lists:
Expanded Vanilla (#19), I Heart Vanilla (#7), I Heart Vanilla: Director's Cut (#7), Graphics Overhaul (#18), Total Overhaul (#23)
These can be found in the 'GH Patches and Replacers' optional file on the main GH download page.
These can be found in the "GH Patches and Replacers" file, you specifically want
10 Atlas - Vanilla BC Mushroomsor
12 Atlas - Smoothed BC Mushrooms. As indicated by this site's own load order, this must come after Project Atlas (which itself comes after the main Graphic Herbalism files).