The vendors need to fill out a really long form to sell any form of potassium nitrate. But for my use, there is no practical substitute. Don't know about your area, I cannot get ammonium nitrate or magnesium nitrate.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738