I'm guessing bulky
fiberglass parts have to go by freight. Many private sellers don't want to bother arranging that. Usually they're offered for pick-up only.
It won't be cheap, but Scamp does know how to crate bulky, fragile items so they arrive undamaged. Two of the same might be nested to save a bit.
Check with Scamp about the fit for rear installation, though- the front and rear may not be interchangeable. At some point they stopped offering a rear full-width overhead cabinet and only install the side-saddle cabinets on new builds now. I'd be interested in their answer.