My wife has nearly finished off her front brake pads. The rotors show some wear, but are not deeply grooved or warped. Can the rotors be turned, or are they only supposed to be replaced?

I only ask because some other European makes don't ever suggest you turn the rotors - it makes them too thin.

If they do need to be replaced, where is a good place to purchase them (mail order, Internet, dealer...)?

Thanks in advance.