If you have a technical college or university in your area, professors there can help you with what kind of engineer(s) you want to talk to. Some of them might even give part of the project to their classes for practice with little or no cost to you. If you need experienced engineering help once you know the type of engineering you need, you can find online engineering consulting listings. Of course, be sure to get and check references.
`NDA` above is Non-Disclosure Agreement aka `CDA` or Confidential Disclosure Agreement, which is a legal agreement between you and whomever to tell the idea to, agreeing to keep the idea under wraps. I`m sure there are good examples online.
If you want to send me a private message with a basic explanation of the product, I`d be happy to suggest a type or types of engineers that could help you.
Success to You!