Maybe I’m late to the game with this, but if anyone is looking for iOS 8 button images and other design artifacts, there is a fantastic resource in the form of a 110MB PSD with every element you could possibly want here:
What’s more, they’re all in glorious vector format, so they scale really well.
If you need to make any adjustments, here’s Apple’s guide on how to produce design elements, including how to think about selected and unselected forms of button icons: