You mean like these from EssexRacing?
I had a set on the 3door and now on the GTR, and nobody does baseplates for either car, so had to make my own.
For the cossie it meant a trip down the scrappy to find some sierra mirrors with plastic baseplates, then a lot of cutting and fibreglassing to make em fit.
With the GTR ive totaly made my own baseplates as its a simpler fit on them.
Gwan mate, Hacksaw, P38 easysand, some screws, and lots of sandpaper, and youl get there, lol