the one I use is called candy chocolate clay. It taste great and is easy to make and use. I have made flowers and little figures using it. the recipe is 14 oz of chocolate chips or candy melts. 1/3 cup light corn syrup. 1/2 tea lorann oil or candy flavor. Melt chocolate in microwave or double boiler. add syrup and flavoring mix til a soft ball forms. Refridgerate to get a little stiff.
I have a recipe from cake decorating school for modeling chocolate - but i believe it may harden in the fridge - have you considered a good old fashioned chocolate glaze? You can get a very smooth shiny finish.....
If you want the modeling choc. recipe, give me your email.
"Sugar, sugar...honey, honey...you are my candy girl..."