For farmers markets during the summer we used to make clay core truffles. Using a dark brown modeling clay available at your hobby store we created the right size spheres and then would coat them in a coating chocolate, decorate them like normal and then spray with a lacquer. In 90+' heat they would last a few months of travel too and from before they started to show a weakening. If you weren't moving them they might last longer.
The only other way we looked into it was to have plastic ones made and that wasn't a cheap option.
I am working on the same scenario right now for display chocolates at the Farmer's Market. We are using PC Marine Epoxy Putty (available at local hardware stores). We spray Pam into the mold before filling with the putty. Let it dry in the freezer. Unmold and spray with a high gloss brown spray paint - looks pretty close. We haven't gotten to the more intricate chocolates yet, but this seems to work for some of the basic designs. Hope this helps!