Abarth do suitable tail pipes -
I believe Ansa also do something similar.
Not sure if either company has UK suppliers. If not, you could always contact them about UK distribution rights and becoming their agent. So long as we're still in the EU of course...
N.B. sorry if this post seems a bit thread jacky but when I submitted it for some reason the only post showing on my computer was the first entry which just says ... I can't find the right parts... Once I clicked 'post reply' the rest of the thread appeared.