These are readily available. There are sold through Napa or you can get on eBay. Basically they are sold with the bearing, because if you are buying a new bearing, you must buy the retaining ring (since the old one was destroyed when taken off). I don't know if you can get the retaining ring by itself.
I think you read it too fast, I did not say I needed the retainer ring that come with the bearing, the seal that sets on the retainer that has the holes for the bolts, the thin seal in the pic is one I'm talking about!