A dichromate / etching process sounds like a great idea ... I think I can even picture in my head how that might work.

As far as creating a -random- reseau, doing it [gasp] digitally would be the best way, especially if the end goal were to be a commercial project. It would be trivial to have a computer generate a random dot pattern, normalize it to obtain the correct color balance, and print the resulting image. There's no reason that an inkjet printer can't be loaded with RGBK instead of CMYK ... This could be done on large sheets, which could then be cut down to the correct size.