Want to make your own? Elizabeth LaBau on about.com has a great recipe. I really like this recipe because she uses dark chocolate.
Pumpkin Chocolate Bark
For this recipe, you'll need orange oil-based candy coloring and oil-based candy pumpkin flavoring--water-based colorings and flavorings do not mix well with the chocolate.
2 cups semi-sweet chocolate, chopped, or chocolate chips
1 tsp pumpkin-flavored candy oil
1 1/2 cups white chocolate, chopped, or white chocolate chips
orange candy coloring
Line baking sheet with aluminum foil or waxed paper.
If you plan to store this candy at room temperature, temper the chocolate. (FYI: you cannot temper chocolate chips). If you are fine with storing candy in refrigerator, chocolate can simply be melted as described in following instructions.
Place semi-sweet dark chocolate in medium microwave-safe bowl and microwave until melted, stirring after every 30 seconds to prevent overheating. (or melt chocolate in top of double boiler)
Once chocolate is melted and smooth, stir in 1/2 tsp of pumpkin flavoring and stir until smooth. Scrape melted chocolate onto prepared baking sheet and spread into thin layer, about 1/4 inch thick, using knife or offset spatula. Set aside at room temperature while you prepare white chocolate.
Put white chocolate in microwave-safe bowl and microwave until melted, stirring after every 30 seconds to prevent overheating. Once melted, add remaining 1/2 tsp of pumpkin flavoring, and few drops of orange candy oil. Stir until well-mixed, and add more coloring if necessary to achieve the shade of orange you want.
Take large spoon and drop spoonfuls of orange all over chocolate on baking sheet. Use toothpick or tip of knife to swirl orange and chocolate together. Try not to swirl too much, or color will become muddy and swirls indistinct.
Refrigerate tray to set chocolate -- about 15 minutes.
Once set, breakbark into small irregular pieces with your hands. If chocolate has been tempered, you can store it in an airtight container at room temperature, but if not, you should keep Pumpkin Chocolate Bark in airtight container in the refrigerator to prevent it from becoming too soft.