What sort of 3D printing? Something like a Rapid Prototyping machine. You can get like powder ones similar to some Z-Corp models, or plastic ones. You can import models from most well known modelling software, such as Solidworks and Rhino 3D. I think this might be a saturated market, depends on your target market. There is one large company that pretty much rules the market for prototyping, and that is Arrk.
I've used autoCAD software which most 3D printers use for the design application.
i think the work you'd get would be across different industry's so my suggestion is a good website that ranks in top of google for search string " 3D Printing "
Best of luck