12x50 binoculars - mount/mods

Hi,
I recently picked up a pair of Nikon Action EX waterproofs 12x50
binoculars which weigh in at one kilogram!!

Suffice it to say I would like some kind of mount for them and have read
about the sky mirror/window device. I am situated in the UK, is there any
place here where I can purchase a flat first surface mirror for such use?
I would make the rest of the mount myself. Anyone found "alternatives" to
astro produced flats - say vehicle windscreen mirrors which it has been
said are suitable?

What about some kind of diagonal in front of the eye pieces? I figured
they would be preceded by some sort of lens and another after the
prism/mirror? I have searched for such item to no avail. Any info? It
could be easier/more convenient than the sky window mount that's the
reason for my interest in it.

Any help/info much app.

Thanks.