Zinc on galvanized steel tends to damp resonances, particularly on the thinnest gauge, which may or may not be to your taste.
IIRC the EMT plates were electrically coated, which made a much thinner zinc coat than hot-dip.
Many steel fabrication shops use protected electroplated steel, which means it is protected on both sides with a thin adhesive film that covers it during all the fabrication process, punching, bending...
I think you should, as been suggested previously, buy your plate from a steel fab, who has access to suppliers that don't cater for the general public.
Now the problem is, if they don't have it in stock, will they want to order it for you? Generally, this kind of supply is subject to significant minimum order.