In a microwave safe bowl, mix together the almond butter, corn syrup, and brown sugar. Microwave for 3 minutes on HIGH. Stir in the milled flax seed and vanilla, then pour the mixture over the rice cereal and mix well. Coat a 9x13- inch baking pan with non-stick cooking spray, then spread the mixture into the pan and press down to form a dense sheet. Let the mixture sit for 5-10 minutes, until firmly set, then cut into bars.