Hi chiod_O,
Have you tried Global Sources? I've used them before for MP4 players. They're a listing of various manufacturers so you're dealing with direct.
Try this here -->
Global Sources - "car dvd player".
I just did a search for "car dvd player" but I'm sure if you change the keywords, you'll probably find more.
They are contacts to manufacturers so require a minimum order quantity (MOQ), but what you can organise is SAMPLES from them so you can 'test' them. Their prices will be better than retail but you don't get to see the product or it's quality until you actually buy it and get it from them.
Hope that helps.