The Sig night sights are some of the best available. Im not sure who makes them, but the ones that came on mine are top notch, both in daylight and darkness. I would get the sights from Sig, if you can, and dont mind shipping them the gun. I dont know that they ship any of thier guns with fiber optic sights, so Im not surprised they are charging you for a replacement.
I have had several sets of night sights from diferent manufacturers, and the Sig ones are the best I have ever used. Well worth whatever you spend on them.