I have done it but its not so easy that it seems.
Eco tuning --> Tuneko Ltd | Aerodynamic parts that lower fuel consumption
People think those things that are cool which save fuel, but they are not:
A. willing to pay from it. they can make their own parts cheaper and usually they don`t care the looks. Even carboard grill blocks are looking OK for 100000$ car in winter...
b. they dont believe that they will save any fuel. so there is not enough data available
c. they have some bizarr reasons not to buy something that saves fuel.
etc
I will do just about all mods possible and have my own serial solutions. With those serial solutions you will need lots of cash to make them reality and still you have to find the resellers etc which aint easy.
There are markets but its not so easy task as you might think of. It would be wise to start as evening job as your freetime and see if there is any real interest. I am willing to help anyone who has the balls to try it in the states.