Like the guys said, a standard wheel bearing will work. I got a cheap one for a hand truck and it works great. It's a 1-3/8" od x 3/4" id flanged bearing. I wrapped a few layers of foil duct tape on the od to snug up the fit in the column. I also dremeled out the center of the old metal colomn cap so it would sit flush on the bearing and help hold it in.
Bill