There are definitely algorithms for UV unwrapping of polygonal models onto texture maps, under various constraints. I'm sure you could persuade one of those to generate you a net from a 3D model.

Here's an instructible on it: http://www.instructables.com/id/Design-Papercrafts-with-CAD-...

Edit: Software for doing what you want here: http://www.tamasoft.co.jp/pepakura-en/