On Mac, right-click on the .app and on the menu that pops up choose "Show package contents". Then there is a "ui" symlink there that will take you to the ui folder which is located inside the app folder under Contents/Resources/ui .

The direct path if you have installed MoI v4.app inside of the /Applications folder is:

/Applications/MoI v4.app/Contents/Resources/ui


Note that on a Mac an .app is actually a folder but when you double click on an app it launches the app and doesn't open up the folder as normally happens with other folders. But to open up an app as a folder you can right click on it and choose "Show package contents".

- Michael