One resource that you might not have thought of... your local auto stereo shop. A lot of cars come with low-end radios, and most of the aftermarket Kenwoods / Alpines / Pioneers / Sonys / etc have backup camera screen functionality... so the shops stock generic cameras and the cabling to run them up to the dash unit.
So give a local one a call and ask... all it costs is the phone call...
I did a radio swap on two prior cars. I got the replacement units from
www.Crutchfield.com - on both occasions I found that they have good stuff and EXCELLENT both pre-sale and post-sale support.
Mike