You can get new lenses fitted for $19 in the USA, unless polarized, then its about $50. Similar prices in the UK, and as stated the Oakley dealer will give you a box which you post off.
If you ever get the chance, go to the Oakley HQ in Irvine, california. Its amazing, like a castle, and in the foyer they have a line of old ejection seats for seating....They'll replace the lenses there and then, or most likely they just give you a new pair of shades....(for $19 or FOC if under warranty)
EA