Recently, I stumbled upon a great website named Icons8. I downloaded their free iOS 7 icons zip file (they also have one for Windows 8 and some other platforms), and, to my amazement found a icon for anything i could through at it. They all were perfectly scaled for the Apple Retina Display. It was great.
I highly recommend this service, and also suggest their paid icon packs for a range of prices if you want to support the developers.
I give Icons8 five stars.
Justin Harbour 