We are the official distributor of AutoID parts in Australia and the mirror covers can be purchased from our online store here.
In order to fit them, carefully pull the existing covers off by firstly prying off one corner with a trim removal tool. Once you have a solid grip of one edge you can pull the existing cover off with a bit of force.
Simply align the new mirror cover clips to the holes and press with slight force to insert the new mirror cover. Repeat for the other side.