If you can't easily find pinapple syrup, you can always make your own. There are a varitey of slightly involved recipes on line, but since usually very little is used in a cocktail, you can make a passable version by simply combining equal amounts of (unsweetened) pineapple juice with granulated sugar, shake well, and let this set for about 2 minutes, shaking again, and then let rest for another 2 minutes before using.