Have an 8" ford I need to narrow. Everyone I have asked so far leads me to somebody else who says no and then leads me to somebody else and so on and so on. I know of Dutchman in OR, but would rather not have to ship them if I can avoid it.
Any decent machinist can re-spline axles. As a machinist myself I'd bet it can be done in under two hours on a basic milling machine with a simple rotary attachment so don't get ****ed in by a shop telling you how complex or expensive it's going to be. There was an article in Car Craft mag (I have it somewhere) about doing a whole rear axle. Another option would be just buying new axles, since shipping is gonna hurt anyway, you might find complete axles for cheaper.
So far every machinist that could do it has said they won't. " we don't work on car parts because of liability." I have a mill, but not a rotary table, or else I would try it my self.