Paint and Body Rear trunk spoiler or tail for 91 GT convertible

The only aftermarket wing that's worth having in my humble opinion:


Don't think it'll fit your vert tho.
 
You could look into something like this:

Nice, but a little spendy. Not sure what to do about the 3rd brake light.

Or there is the 92-93 special edition style wing (the cervini is similar):


Or just do what was mentioned above: Get a plain coupe trunk lid and swap them out. That is how I got rid of the hideous luggage rack my coupe had on it.