Can't buy new.
Here's your options:
1. Check with the major yards specializing in C-bodies (Murray Park, Wildcat, etc). Shipping will hurt.
2. Find a %$#^box on your your local Craigslist, check it out, if it has a good quarter, drag it home and break out the SawZall.
3. Fab from scratch. I'm no bodyman by any stretch of the imagination, but I got it done somehow.
I have also figured out that someone before me had removed the vinyl top and the chrome around the bottom of it but that is okay I will be repainting her in B5 blue and I will paint the top white to make it look like it did when it had the white vinyl top