All three, Bostick & Sullivan, The formulary and Artcarft will sell you the chemicals to make a dry plate, not dry plates themselves. I would suggest you visit WWW.thelightfarm.com for information, formulas and to see how they do it. They also have an excellent reference section on books about emulsion and dry plates.

Also the silver gelatin emulsion making thread on APUG has lots of information ifyou dig for it.

Joe