Looks like the 240sx (and likely other models) used the same 12v socket and the light-up trim ring, and there are some on eBay, but they're stupid expensive for what they are. Looks like it would be pretty easy to mount an aftermarket 12v socket in its place. I may end up doing that myself, as mine's starting to crumble too.
Your clamshell's condition is pretty typical, unfortunately. I fabricobbled a replacement from sheet metal for mine. I'll keep an eye out the next time I'm at the wreckers, though, on the off chance.