London Underground 1938 stock guard's pilot lamp

We saw this at the London Transport Museum in Covent Garden. It's a clear pygmy lamp with a blue painted end and was used to indicate to the guard that all the doors were closed and it was safe to signal the driver to start the train. I have been searching for one of these for 40 years, I even asked the curators at the museum, but they didn't have any more :-(

Does anyone know of a suitable paint that I could dip a clear pygmy lamp in that would allow me to replicate one of these lamps..? It would obviously have to be able to withstand the heat.