Don't know about those packs but you should go to an elevator if you want nitrates. You know, where farmers take the crops in to sell with the big silos and grain legs. They will have a lot of the stuff you would want for refining, like Lye (Sodium Hydroxide), Sodium Nitrate, Potassium Nitrate, Soda Ash (Sodium Carbonate) and so on and if they don't have it they can probably order it. Usually they get the products in 40 or 50# bags which would last a long time. One bag of the Nitrates shouldn't raise any red flags with them but if they ask what your using it for just tell them.
Steve