Replacement passenger wing mirror

Hi there.

Having had an unfortunate confrontation with a telegraph pole (best not to ask), I need to replace the passenger wing mirror. I'm trying to do it via the component parts and have got a mirror cover, mirror and indicator light on eBay for not much money.

The only piece I need, I think, is the triangular bottom cover, which I can't seem to find anywhere on any parts site. It's the one shown in the picture at the bottom of the mirror. Annoyingly the one on the car at the moment is cracked. 

The connecting unit and mechanics are fortunately OK, so it's just the external parts which need to be replaced. Does anyone know where I can get hold of these particular parts?

Thanks in advance!