Metal enclosure for custom car stereo project
If you want one that is ready made and bare (not populated) I think what you want is a car stereo housing. They don't make them just for DIY that I know of, but they do make them as replacement parts. Here's an Ebay listing for one, just for example. Here's one in the UK. Try searching for terms like "car stereo housing" possibly with "replacement" or "repair". If you want a faceplate a similar method should work. "Mounting frame" or "cage" are also used in some instances. I think Kenwood sells several types.

They also sell trim kits, which are intended for framing a unit installed in a new hole cut in the dash, and under dash mounts, which are basically a tub to hang it in a new location. These probably aren't what you're looking for.

But, if I were doing this I'd look for a cheap, used, or broken car stereo that fits my car as a starting point. Then you get the housing, connectors, and faceplate, and probably some other stuff you can reuse as well, like maybe filters, regulators and an LCD.