Upon further reflection, those tiny universal aluminum hubs look way too small (only about .8 inch outer diameter and max 6mm shaft). I've been looking for hubs all afternoon and can't seem to find much at all. So far I've found these:
Packard Fan Hub - 1/2" bore, 2 set screws, 3 mounting holes. other specs unavail. $3.96
Chicago Die Casting 2122 1/2 Die Cast Hub - 1/2" bore, 1 set screw, 4 mounting holes, outer diameter 2.75 inches, $4.99.
I was rather hoping for a considerably larger hub -- maybe 6" outer diameter. I can't believe hubs are so hard to find.