Sounds like a market opportunity for some enterprising Cypherpunk. So Doctor, where do I get cowpox?
From cows, of course! Edward Jenner, in the late 1700s, noticed that milkmaids tended to have resistance to smallpox, so he took some cowpox pus from a milkmaid named Sarah Nelmes, and injected it into a boy, who then became immune to smallpox. You would have to do some research into cowpox to see what is the best way to do this, and where you might find infected cattle. Modern cattle raising is probably a lot more disease-free than it used to be, but maybe you could find samples in less developed countries. I would imagine you could buy some cowpox cultures from various bio research supply companies, but that would probably attract a lot of attention these days.
Even earlier, Chinese doctors found that they could achieve resistance by snorting dried pus from smallpox victims. Drying it must have been enough to inactivate the virus. There is so much literature (going back hundreds of years) on smallpox that it should be pretty easy to come up with a safe, reliable recipe. The problem now is that you will attract a _lot_ of attention trying to buy the ingredients, so you may need to be sneaky about it. Even buying plain old lab glassware requires a permit these days (thank you War on Drugs!). It does sound like a good biz opportunity, but you would have to do it all in a country without liability laws or an FDA. It might be hard to find a qualified biologist willing to do the work, and it would be hard to find a host country for this, because they would be accused of sponsoring biowarfare research.