I have them made to my specification. They can be purchased from the Photographers Formulary. I am making no profit on these as opposed to several comments here to the contrary.
They serve several purposes in coating paper:
1. Heavy weight to reduce lift and chatter in order to give a smooth coating.
2. High heat retention to keep the melted gelatin melted! This reduces the problems with varying coating plate temperatures.
3. Stainless Steel (308 or 316) to prevent contamination and corrosion.
The doctor blade (as it is properly called) was used in the trough coater shown here on APUG in one of the videos. It was used to even out coating nonuniformity. Another design is used for film, and yet another for plates. These latter two are not currently available.