I have never made a wood bearing for a disc, so I could be wrong. But see what would be good hard wood, you can get your hands on. May have to glue pieces together to get a block and then find a whole saw as close as posable of the size you need. Then very careful use of a die grinder. That is if you really have your heart set on using this.

But that looks like really nice yard art. 

Reaching back in my memory banks from my sawmill days I recall that we used wooden bearings on the augers in the sawdust bins; the bearing supplier told us that wooden bearings were still the best in certain low-speed applications where abrasive stuff was being handled.

I did a google search for "wood auger bearings" and got literally dozens of hits; there are many suppliers such as McMaster-Carr, Motion Industries, All States Ag Parts, etc. Also numerous custom makers.

When I taught Vo-Ag, we made straw walker bearings for several farmer's combines.  Good project for the students. The students utilized their skills on drill press, mill, lathe and other tools.