graphical files are pretty much everywhere. though, you can use the names of folders to predict what it is.
for example: /data/menu/bustup is sprite art, because you see the character from the bust upwards. the images are inside the .xa files in most cases. the images themselves are .xi files. inside the .xa files, they are named 001, 002, etc. you can extract them with Karameru, right click it, choose edit in Kuukkii, and thats how you view/extract an image.
i dont really remember where i found medallium icons, but to make it easier to navigate, set your os to open .xa files with Karameru and .xi files with Kuukkii by default. it just takes a while to find things.
(btw, .xc files are to do with the camera i think, so they wont be of use for this case.)