The graphics in the \graphics\menu\home folder should be the ones you are looking for (took me forever to find them first time - due to them not having an arrow in the graphic

)
Each one is made up of a left, middle and right graphic (like most graphics in the game), the middle one will be created over and over to fill the space between the left and right buttons, so each button only needs a width of 1 pixel unless you are doing anything fancy.
button_left/right/middle is the default state, button_over is when you hover over it, clicked and disabled are obvious, cannot actually remember what state showing is.