All of the AC pulley bearings can be replaced, including the one that is riveted together. The bearings, in the US, are readily available and used on a wide variety of vehicles and equipment. They are “6202” bearings if you’re searching for them. Stay away from anything Chinese made or you’ll find yourself replacing them quite often as they fail quickly.
For the idler that is riveted- cut the rivet heads off, use a punch and hammer to drive the rivet bodies out, separate the pulley halves, press the old bearing out and a new bearing in, and rivet it back together with a nice, strong rivet. Be careful not to warp the halves if you use a vice instead of an actual press.