However, if you can't find dark corn syrup you could use light corn syrup or even golden syrup. (joyofbaking.com)
For this recipe we are using dark corn syrup, which has a caramel color and flavor which gives the syrup a deeper flavor than light corn syrup. (joyofbaking.com)
If I were to make it again, I think I would stick with bittersweet chocolate, and only dark corn syrup. (epicurious.com)