your dealer wouldn't help you? My brother deals with GM factory Cd decks and CD changers. I'll see what he can do for you -and I can gauruntee it'll be cheaper than the dealer.
Also, if you can get the part # go to www.gmpartsdirect.com
if you want a new one (plus this website also gives discounts up to 60% off the dealer price) . Also verify that your car has the CD changer cable installed already -if not you'll want the part # for that also.
PM or e-mail me if you want my brothers contact info.