I tried my dealer (Hexagon of Highgate [Parts and Bodyshop in Kentish Town]).
I wanted to change the chrome bonnet scoop to a body coloured one and get the aero grill on mcs bumper.
After they looked at me like I was a f'ing idiot for wanting to do it, they sold me the parts. They would fit and paint the bonnet scoop and would do the top bit of the aero grill but not the bottom bit which needed modding before fitting. They said as it wasnt standard or authorised, they couldnt do it.