Dealerships usually keep scrap metal, and a scrap guy will come buy and pay for the scrap to take it to be recycled. old pads just get throw away.
depending on how long ago, and how they handle their scrap metal, they might still have his parts.
now its not the thickness of the rotor they are measuring.
The dealership is saying in order to machine the gouges off the rotor, they will end up machining past the minimum thickness. So its not that they are past their thickness, its that they cant machine them properly.