It is going to be much easier to make your own.
The following are recipes are a starting point for porcelain and bone china
Porcelain is made from 60% china clay, 20% feldspar and 20% quartz,
Fine bone china is 50% bone ash - which adds strength, extra whiteness and translucency - 25% china clay and 25% feldspar.
Plus of course a deflocculant New Zealand China Clays Ltd mine and manufacture the whitest china clay in the world and is marketed as Ultrafine China Clay. It is exported to twenty countries and should be available in the US.
Web site
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analysis is
Ca 0.07, Na 0.06, K 0.05, Al 35.8, Si 50.1, Fe 0.28, Ti 0.08, Mg 0.06
As you cab see the impurities ofiron and titania are very small
You may find this link interesting
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Two side bars
I have been using a white stoneware clay. In oxidation it is dead white, in reduction it is a non descript grey.
If you make up a porcelain slip you can add toilet paper to make a paper clay. You then can pour it over a plaster or glass surface to get very fine translucent sheets.
Could this be called 'casting' about for information
John W