In the bowl of a food processor, process maple cookies and walnuts until finely ground. Set aside. (You may have to do this batches if you have a smaller food processor)
In a large bowl, sift together powdered sugar, salt and allspice.
Stir in rum and maple syrup.
Add cookie and nut mixture to the bowl and stir well to combine. Cover and refrigerate for 30 minutes.
Scoop out tablespoon sized portions and use your hands to roll into balls.
Toss in maple sugar to coat.
Place on baking sheet and refrigerate for 30 minutes before serving, to allow the sugar to adhere.
Notes
Instead of maple sugar, you can use 1/4 cup granulated sugar mixed with 1/4 cup light brown sugar to coat the rum balls.