Line a large baking sheet with foil, and coat with cooking spray. Insert 1 (6-inch) white dowel into stem end of each apple.
Combine sugar, corn syrup, water, and candies in a small heavy saucepan over medium heat. Cook until sugar dissolves, stirring occasionally. Cook, without stirring, until a candy thermometer registers 300° (about 8 minutes). Remove from heat.
Working with 1 apple at a time, holding apple by its dowel, dip in syrup, tilting pan to cover apple. Turn apple quickly to coat evenly with syrup; let excess syrup drip back into pan. Place apple, dowel side up, on prepared baking sheet to harden (about 5 minutes).
Apples sold in bulk in bags, which tend to be smaller than those sold individually, are the ideal size for these treats. You'll find white dowels at hobby and craft stores, or use wooden craft sticks. Store Candied Apples in an airtight container for up to three days.