Best guess, that is an SF6/T2 45mm lamp and from your observations and Keith's info on the spec, likely 10/300mA or thereabouts which would match the ~3 watt spec.
I will look some more, armed with the additional info. BUT there are a lot of factors weighing against finding one:
1) 10V is much harder to find these days; many lamp makers have stopped making them.
2) 45mm length in an SF6/T2 lamp is a real corner case, also not likely anyone is still in production on those. More common lengths are more like 28-29mm, sometimes shorter. They also did 31, 37 etc. but mostly today you can find stuff around 28-29mm long and not much else.
I can think of a few ways to solve that though, one would be to use GF740 12.6V/300mA fuse lamps that are 28mm long, and make a fitting using the old end caps to extend the length out to 45mm so they still clip in the same way. the end caps can be soldered so reusing the original caps plus a short piece of copper rod (romex etc.) would work. Should provide roughly the same amount of light but the filament won't be as long, which may show up as weaker light at either edge of the meters.
With that much length you could also probably fabricate an in-line LED plus resistor plus diode arrangement that could be clipped in place, with a few LED's to help spread the source out a little. With a lightly frosted diffuser, that might actually look ok though I am no fan of LED's used in meter applications as a rule.
Another solution could be to move the clips closer together to allow use of a "standard" length lamp. Or, move 'em further apart and use a pair of 6 volt 25mm long lamps soldered end to end and clipped into place - assuming those can be found with the correct wattage rating. That would help with the short filament issue, whether you'd notice a gap in the center where the two end caps were butted together, I don't know.
Sure glad they didn't use that type lamps in my 5L15 integrated amp!
John
