sim tray lost

yes, sadly i have lost my sim tray. I was traveling to US and to make sure i wasnt roaming or using 3G i put the sim card out. While in the process i have lost the sim tray...

Is there a warranty promising that if i lose sim tray the apple would restore it back?? or do i have to buy it... If i do have to buy it could you please post on where and how I can get the sim tray?

Thanks