....and where can I find it?

I'm looking for a bar about 10" long with several diameters (largest I think is 1"). It has a flat ground to C/L.
It's a great tool to align a 4th-axis rotary or set Lathe tooling to C/L.
I don't know the name and can't find it with a search engine so I can buy one.

Anyone?

Thanks.