The guys on Practical Machinist are talking about ceramic ball bearings for racing cars, motorcycles, etc. You might start with ball bearing suppliers and work backwards.
An oil well proppant is pumped down oil wells to keep cracks underground open so that oil can flow to the well more freely. It needs little pricision in size but has to be cheap. There are companies that make it from fly-ash but I'm not in that business. A google search would seem to be appropriate, or ask the question in the petroleum production forum.
for the ceramic ball valve. Hope this website will be your solution. Or you can email to andybear513@hotmail.com for the electronic brochure of ceramic ball valve (material:zirconia+alumina ceramic)