Potassium nitrate

i'm new to this forum, i registered because i need some help. I'm not interested too much in chemistry but i need some help. I need to find KNO3 known as Potassium Nitrate. I need it to make a smoke bomb :P like the ones on youtube. I found out that Potassium nitrate is Saltpetre but when i searched for it in the chemist's shop they told me that their saltpetre is with amonium nitrate. Is there any way to find potassium nitrate ?>

another question

I found some powders at my old house, it used to be my grandmothers, she was a teacher.. the point is .. there are few plastic bottles with white powder and one of them is potassium nitrate but i dont know which one. How can i find out which one is KNO3. Btw i know that there is pottasium nitrate in one of those bottles because its written on a peace of paper but its not sticked to the bottle, :/
Please help :P