I remember seeing various nut butters at Michael-Angelo at Hwy 7 and Woodbine. I don't remember specifically if there were pistachio butter though.
I was just in Food Basics the other day and saw a pistachio paste type of product. It was a Lebanese product with several other Lebanese products ... in the canned soup aisle.
I think i read that it was a dessert paste (ingredient list had sugar near the top), but it seems similar to what you might be looking for.