Is there a spray out there that I can buy and spray on a modeling chocolate figurine to make it harder or stiffer?
Do you mean Chocolate Freeze Spray? It is in a aerosol can. I'm not sure whether it works with modelling chocolate, it is usually used to instantly attach one chocolate piece to another. If your figurine is softening because it is too hot in the room it is being stored in, anything like this kind of spray would only be temporary.