Well, I've never had to replace that bearing, but here's a picture.
Looks like you have to replace a bearing within the big pulley. Or maybe the noise is from the clutch (outside of the pulley, the clutch assembly doesn't spin when the AC is turned off). When you get the belt off, maybe you can pinpoint the location of the sound.
This parts-picture implies the DEALER won't have the bearing alone, you have to get the pulley or the clutch assembly as indicated by the part number pointers. But if you can press out a bad bearing you can check bearing-supply shops. This picture is a bit strange, where #2, #10, & #13 show alternate combinations of the same parts that you can buy packaged together.
If the bad bearing were INSIDE the compressor, then it would be noisy only when the compressor is actually spinning. When the AC is turned off, the pulley is freewheeling on it's own bearing outside of the actual compressor.