Update
As usual, what you want often turns up.
I found a reasonably correct BM4 ammeter in excellent condition...
I say "reasonably correct" as it is not a 30-0-30 unit, but that's a practical concession that I can easily make.
It has the less 'stylised' needle that CSX2124 and others also have.
I also found the correct Smiths fuel gauge to match it.
Cheers,
Glen