When you reference "", what era of emulsion making are you thinking of? In the beginning, there was no sensitization. That was followed by red food coloring, and then a fast-moving wave of chemicals that came and went -- with slight variations among Kodak, Ilford, and Agfa. (Fuji: I don't know much about.) Anyway, I don't think procuring sensitizing chemistry that would have been familiar to emulsion makers in the 1920s is much of a problem. I'm using a number of them.