For this project it probably makes sense to start with the companies the others mentioned. Recommendations from others have been the best way to find good manufacturers. When we don’t have sources available google is a slow way to go but it will usually get you there. The most time consuming part is following up with each company to get a sense of what they’re really capable of. Be sure to get multiple quotes; you’ll learn something from every company and like was said earlier quotes can be all over the place.
Another resource is http://www.mfg.com. You upload your part drawings and models to create an RFQ and manufacturers bid on the project. It’s not ideal if you’re trying to keep the design secret before launch, but we used it once and did end up getting in touch with a couple decent seeming companies. Fortunately you don’t have to buy through the site; you end up dealing with the company directly. It’s just a matchmaking service that manufacturers pay to be on.
I also get advertisements for a traveling trade show call “Design-2-Part” (http://www.d2p.com) which features contract manufacturers. The advertisements seem a little hokey for some reason but I recently talked to someone who went and they said it was well worth the trip. Theoretically there’s also Thomas Register (http://www.thomasnet.com), but I find it clunky to use.