If you are looking for the big rubber seal that goes on the backside of the knuckle, you can get them at Advance Auto parts. I have bought them there before.
If you are talking about the metal pieces being in two pieces, then that is how they are supposed to be....both the inner and outer metal pieces are a two piece design. Not sure if you can get them at auto parts stores or not....I would guess not and that they would be a dealer or vendor item.
IMO, I would not replace the wheel bearings, unless they are worn or damaged. Just clean them up, repack them and reuse them.