How does one get to design electronic props for movies or Broadway?

So many questions here, but mainly: How would you get to design electronic components for sets/gadgets in movies? I’m am an Electrical Engineering student.

ie. I saw an extra for Harry Potter HBP where a guy said his team spent two months building a little robot that looks like it’s knitting in mid-air. Whoa, do I want to go to work and do that? Yes.

So I’m wondering how people get those jobs, aside from luck of course. I don’t even know what kind of company they would work for. Warner Bros. (Who makes the movie) or Time Warner? But I don’t see any positions listed in their careers that involve building whatever is needed for movies or shows.

So, if you know much about the movie industry, are there third parties who contract out those services, or third parties who design and build custom props and robotic elements? If so, what are these companies? I don’t know how to begin looking for them.

This goes for Broadway productions as well. Who builds the electronic components of those sets?

Thanks in advance.