Unless you were talking about where to get the holders for the lights... which I couldn't find for a reasonable price... so I just went with sticking a 3mm blue LED up the center of the button, insulating one of it's legs to avoid a short, and wiring it in series with a resistor to the voltage for the leaf.
I think it turned out pretty well... even in a well lit room you can tell the buttons are lit. I was at the arcade when the Robotron was getting worked on (it not the arcades, it's just on location there) and I thought it had been missing it's lights this whole time... turns out the lights where there and going well... but I couldn't even tell the buttons were lit up, and that's in a "dim" arcade.