Have a look in London first.

Red Dot cameras.
Aperture UK - near British Museum
Robert White.
There is place on the Strand near Waterloo bridge (I forget the name).

If you dont get it serviced when you buy it, you will need a service within a few years. I prefer a service when I buy it.

They are all good. My preference is M3 for 50mm lens. I have the .85 viewfinder on the M6 which is good for the 75mm and a .58 viewfinder on an M7 for wide angle lenses.