Restoring default firmware to AT&T w580i

I've had my w580i for around a year and a half, and just recently upgraded. When I originally got the phone I did debrand it to get rid of the crap proprietary AT&T frimware, but now I'm looking to pass it off an want to restore the default firmware onto the phone. I'm sure I can find a guide for flashing the phone online, but what I do need, is the default AT&T firmware. Is there anyplace anybody knows that I can download this to restore it back to it's original firmware? Any help would be great.