I looked up a couple of Blaupunkt units that support dimming today, but it was on-or-off dimming, not variable-with-the-dashboard-control dimming.

The Kenwood KDC-6007 in my car is already dim, it doesn't need additional dimming. It's hard to read in the sun. I was thinking about replacing the backlight bulbs with high-brightness green LEDs but I wonder if that'd really help.