I receive a number of evaluation samples, but I only recall one that was a pre-production model. That one never made it to market. Many of the others were first run models from early in production, but always fully labeled and such. I've also been contacted for input and feedback during product development, but never with a prototype other than that one time.
The best way to receive samples is probably to be an instructor or coordinator of a CPS-related organization and have a business card. Some companies, especially smaller ones, will offer samples (if you inquire) for evaluation at conferences like Lifesavers or KIM and often ask only for feedback or possibly a review in return. I was always very diligent about doing so. Other companies and distributors will often give away their floor models or raffle them. As is popular in the tech industry, having a popular blog or base of reviews at a website like epinions (or Car-Seat.Org!) is a another way to get some attention for potential samples. Not quite as common for child restraints as it may be for computer processors, but it might be worth a shot.
I have been contacted a few times for recommendations on who might be a good participant for a review/feedback. I often refer them to our reviews forum to see who has written some of the better ones;-) Technicians and Instructors can also sign up in the Tech forum to post reviews and commentaries on our blog at
www.carseatblog.com . That blog could really use a jumpstart and it's the trendy way to reach parents in terms of advocacy right now, too.