I get most of the usual stuff from Bostick & Sullivan and the Photographers Formulary, as suggested above. Silver Nitrate was difficult for me, but I got some last year from JDPhotoChem outside of Montreal. I believe, however, that they are now defunct. You might get a suggestion from Bob Carnie of Elevator (apug sponsor here) or possibly Mike Wilde here, who I believe was in touch with JD before she went under. Mike could probably outline the procedure for manufacturing silver nitrate, I'm pretty sure.

Good luck. I've been using mine for experiments with salt prints and with making my own Van Dyke Brown concoctions, and it would be useful for me to know where to source more when I need it.