Probably everyone but me already knows this, but I still read questions about KNO3 availability. See the following comments relative to 14-0-45 KNO3 fertilizer and KNO3-based Stump Remover.

Stump-remover grade product must first be thoroughly washed in methanol to remove the coating. This is necessary, not only to enhance performance, but to ensure that melting process safety is maintained. Complete drying in an oven for a minimum of 1.5 hours at 200F is then required to remove residual moisture. Note that Wilson'sTM Stump-remover was the only product tested -- other brands may differ in composition and suitability for use as a propellant oxidizer.

Fertilizer grade product must be dried in an oven for a minimum of 1.5 hours at 200F to ensure that the burning rate and performance is optimized.

To ensure optimal performance, chemical grade product should probably be dried in a similar manner to remove residual moisture, even though earlier testing indicated that absorbed moisture is less than one percent.

Also, the synthesis of KNO3 from AN is fairly simple. See:

http://www.nakka-rocketry.net/knsyn1.html