If you can get a very high quality silver and nitric acid, you can make it very easily. I've made it by myself and so far no problems with it. My silver is "99,9%" and nitric acid was probably reagent grade, now I have even better trace analysis grade. Contaminants might be a problem, but it may be better still than no emulsions at all. Process is simple: just dissolve some silver in nitric acid at about 70 C (almost the boiling point of nitric acid). Just be very careful with nitrogen dioxide fumes! Make sure that all the silver has dissolved at that high temperature, add nitric acid if not. Then boil the acid away, silver nitrate starts to precipitate. Boil as much acid away as you can, add some distilled water and boil it away again and repeat. Then boil all the water away carefully until completely dry. Remember good stirring. It takes many hours.
Disclaimer: this is how I did it and I think it succeeded. Please correct me if there are errors.
There was a link here to an old, war-time documentation of Fuji's process to remove impurities from silver nitrate prepared this way. It says the result is usable for emulsion making. It didn't sound like too difficult of a process.