Alternator bearing replacementcost

Hello everyone I’ve found out my alternator is making a sort of hum or whining noise and I’m suspecting it could be the bearings making the noise? I figure it’s better to try changing out the little things before buying a whole new one, but the problem is I can’t find a site that sells bearings for my car alternator, I checked autozone and o Riley but couldn’t find a bearing that fit my car alternator, and I’m just unsure if any sites I’ve never not found a part at autozone or o Riley so I feel stuck. My car is a 2007 Pontiac Grand Prix, if anyone knows of legit or good websites could you please let me know!