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#48100 Chemical description:Pigment Red 101.77491, Fe2O3CAS No. 1309-37-1
#48120 Chemical description:Pigment Red 101.77491, Fe2O3CAS No. 1309-37-1

Since they are listed as chemically identical,...

This is 0.25 micron cerium oxide, from Neil Miller's strop-shop.co.uk. If you do get cerium oxide read the MSDS sheet linked at the bottom on the linked page.

There doesn't seem to be anyone...

Look into Iron oxide, Cerium oxide, and CBN as finer grit abrasives. Of those CBN is probably the smoothest.
You can use mineral oil to make a thin mixture like paint. For a thicker past use...