Well, to start with, you want to know what to buy. Wikipedia can help you here:
You want to know where to buy them. That’s a little trickier, you may be able to get them at bakery supply stores or other restaurant supply stores, if you can find them locally.
You want to know what each one does, Wikipedia can help, but I’ve heard of a few, so I can give you the 2 cent description. BHA and BHT, for example, are antioxidants, that is they oxidize so easily, they protect fats from oxidizing, and ending up tasting rancid. Propionate inhibits some molds, benzoate inhibits some bacteria.
I’m guessing you want exact amounts of what to use and when. I don’t think you’re going to find that online. Maybe you can find some general info in a university level Food Science textbook, but the more specific the information you need, the more complicated it will be, and the more background information you’ll need.
Basically, if you needed it, you’d know everything there is to know already. These chemicals are used in vanishingly small traces. Maybe mixed in with the flour in mg preservative to 50 lb flour. You may not be able to use them properly on your own.