Radio power / volume knob

This will sound daft (most of my posts do).
The on-off / volume knob has gone missing from my original fitment radio cassette CD player on my '93 SW20. My own fault it had got cracked and loose and I kept meaning to fix it up with some filler but never got to it and the last time it fell off it vanished for good.   Grrrr.
So does anyone a) have a spare one lying around that they'd sell me or b) a suggestion as to where I can find a suitable replacement. Would like to retain the original look rather than put on a Jaycar generic radio knob with a grub screw.
Ta,
Graham