What about calling a place like Catto? I'm sure they have made a lot of custom pieces for people and might have an idea of what you are looking for. Here is a link to a spinner list:
There are other examples of spinners that look like what you might be after. For example the F1 Rocket spinner? Now that I've suggested an F1 spinner there will probably be someone to kindly let us know that won't work, but hey, at least that will help move the conversation along
In the meanwhile coll F1 pics are always worth a glance for eye candy.
I had a list of aftermarket aerodynamic and cool mods for RV's that was good in 2013 when I was involved in an RV-4. A lot of these links are expired now. I guess that's the nature of cottage industry and also the temporary nature of web addresses too. I bet there are a lot of options out there!