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I found mine on Craigslist. Paid $75.
I don't know if it's the right size, but I think there's still one in our shop from an '08 F150. It's from a regular shortbed, not the super shortbeds that a lot of 1/2 tons have now. It is solid with no windows (except for the one up against the cab) and the rear window/door frame is bent.
There's one out there. Be patient. It took me a while to find mine.
Just be aware that when you do find one, depending on the make, it may be obsolete. Mine is a Stockland, and they went out of business years ago. It's a well-built-solid-unit, but to get parts for it, well, you can't. If a window gets broke you need to have it custom made. The seals may be available, but you need to cut a piece off of one for a reference. The locking handles may not be available and will need to fabricate something to make new ones work. Not big issues, just something to keep in mind when you find an old shell to buy.
I got a really ugly one for you but the distance may be a problem. It's got a nice green tint right now. It comes with a 4X8 sheet of plywood bolted to cab and top. Good for putting a grill, lawn chair, cooler up there and having a cook out. Your neighbors will really be envious.