My first thought runs to ceramics and the temperature 'cones' used in kilns for clay work.
My second thought is that perhaps industrial catalogs like Grainger or McMaster-Carr may have either what you are looking for or can give you a pointer in a direction toward helping find a source.
Another thought is scientific supplies of some sort.
The blast furnace industry probably use calibrated infrared based cameras to measure metals just prior to pouring.
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