How do I search all subdirectories to find one with a certain name?

Try find /dir -type d -name "your_dir_name".

Replace /dir with your directory name, and replace "your_dir_name" with the name you're looking for.

-type d will tell find to search for directories only.

For a more general solution of finding one or more directories and searching them for something like finding old email addresses in git repositories look at the following pattern:

find . -type d -name .git -print0|\
    xargs -0r -I {} find {} -type f -print0 |\
    xargs -0r grep -e '[email protected]'