The Cake Bible by Rose Levy Berenbaum has a recipe for it and here's one for Wilton's candy melts - a cheap way to experiment
14 oz. package of Candy Melts
1/3 cup light corn syrup
1. Melt Candy Melts following package directions. Add corn syrup and stir to blend. Turn out mixture onto waxed paper and let set at room temperature to dry. Wrap well and store at room temperature until needed. Candy Clay handles best if hardened overnight.
To Tint: Candy Clay may be tinted using Wilton Candy or Icing Colors. Knead in color until well blended.
To Use: Candy Clay will be very hard at the start; knead a small portion at a time until workable. If Candy Clay gets too soft, set aside at room temperature or refrigerate briefly. When rolling out Candy Clay, sprinkle work surface with cornstarch to prevent sticking; roll to approximately 1/8 inch thickness.
To store: Prepared Candy Clay will last for several weeks at room temperature in a sealed container.