Mike, these are hard to find. i have only seen one go up for sale (by itself) in the last 3 years ... and it was expensive. you might reach out to munich alex on this forum to see if he has one, or can pick one up if he runs across one. he deals in these things more than most.
your best hope is that somebody has a petri with corrosion on the spokes and is willing to part with something. the corrosion is virtually impossible to get off of the spokes.