I don't think there are many dealers that would carry a lot of those kinds of parts this side of Scoggin' or the like. I believe there is an actual list of GMPP authorized dealerships listed on GMPP's website. Maybe have a look and give them a shout.
"...What IS true: We anticipated that this would happen - we are never finished - and yes, Ford DOES deserve to win now and then. To think that GM can come out with a car to make ford throw in the towel is simply foolhardy..." - fbodfather