Where to purchase authentic OEM iphone4 back glass?

[G60]

I'd like to sell my old at&t iPhone 4 (not 4s), which is in almost new condition aside from some scratches on the camera lens which render it almost useless, and i'm looking for a reputable dealer for an OEM back glass panel.

All googling has done is made me weary of fake plastic panels being sold as OEM, and a bunch of shady looking sites that I don't feel comfortable giving my CC/paypal info.

Any assistance?

EDIT: Upon further googling, I'm reading that I can make an appointment with my local apple store, and they can replace the back glass for $29. Is this true? If so i'd rather do that then chance buying some garbage part just to save a couple bucks, I'm not the type that wants to rip off whoever ends up buying the phone.

[JDay]

EDIT: Upon further googling, I'm reading that I can make an appointment with my local apple store, and they can replace the back glass for $29. Is this true? If so i'd rather do that then chance buying some garbage part just to save a couple bucks, I'm not the type that wants to rip off whoever ends up buying the phone.

Why not call them?