These tubes are on the expensive side these days, but it's possible to make some credible modern substitutes using sub mini's inside test tubes. It's a job that takes some crafting but I think it would be very satisfying to do. There are a number of sites on line talking about it and there's a thread over on ARF now on it. The type of mini and the filament resistor would vary per the original type tube being replaced. This describes the basic technique:
http://antiqueradios.com/forums/view...p?f=6&t=211281
Also for not much money you can make a small solid-state power supply to tuck inside the cabinet. There are a number of diagrams on line showing such supplies for twenties battery radios, farm sets, etc.