Go to a CTS forum and find a quality vendor that sells OEM parts. lol at the aftermarket joke. If oem is made to last, why is he replacing it? Things go bad and as long as QUALITY is a priority then there shouldn't be a problem.
I've used both of edd's suggestion and got good pricing + service.
send me the vin number for the vehicle, i will get you my cost, i work at a dealership, also how many miles are on the car ? might still be covered by warranty, also what makes you think you need rear wheel bearings ? the rears seldom go