One place I would recommend you try is a company called TomCO2, located near Atlanta, GA. They specialize in CO2 equipment, such as vaporizers, storage tanks, cylinder filling pumps, dry ice pelletizers, etc. You will probably find them and their address in Goggle or in the Thomas Register.
I don't know why you want to vaporize CO2 for, but you might not need to pay somebody to do something that easy. All you need to do is to create a pressure drop (orifice plate) and you have a nice mixture of gas and dry ice released.
The diameter of the orifice will depend on your supply pressure and what you want to get after the orifice.
This is very well documented. There are few threads on the topic.