First, you will need more than an idea. At the very least, get a first version of the design, as well as a general description (intended use, etc.) on paper.
Second, before sharing the design with anybody, make sure to have a solid agreement in place that targets all the usual risks (not your standard non-disclosure agreement).
Third, you might go in the wrong direction and spend many months working with the wrong type of suppliers and, in the end, get nowhere. Talk with a company like ours. We have worked with a number of people who were in your situation.