Alex Coleman ) gurgled happily, sounding much like they
were saying :

I want to mount a mirror on the side of my desktop PC so I can see
through the window to my side without moving my head.

A car overtaking mirror seems ideal and I want to mount it such that it
can swivel and be adjusted. A ball and socket would be nice but I don't
see many of these available.

(A spiral wound metal arm has too much "spring" and springs back a
distance to where it was moved from.)

Where can I get a ball & socket which has a decently wide range of
action?

Why not just get a "Monitor Mirror"? They're purpose designed for exactly
that. Most of the cheesier PC suppliers will have 'em for between a fiver
and a tenner, or you can often scrounge 'em free-but-branded if you go to
computer industry trade shows.

Alternatively, think classic car mirror - the type on the end of a steel
bar-type arm. £25 or so should sort you with something that'll have as much
adjustment as you need, and a nice easy mount onto the monitor.