OK, I was thinking that these (like on my machines) would be two piece "wedge" bulbs #400 (for the big 'uns) and #85 for the subminiature small ones. (this is where the bulb comes out of the base that screws into the board). There are LED replacements for those exact bulb sizes in 28vdc as well.

If it's an "all-in-one" bulb (i.e. the bulb is wired and soldered in directly to the base) then I am thinking you could either McGuyver it by yanking out the dead bulb and attaching a new wedgie bulb with a little artful drilling and soldering perhaps. OR If it's possible that the base is the same as Instrument panel lights (but matching the voltage is going to be harder unless the led accepts variable voltage - as some do).

Unless maybe you can substitute a different twist base that accepts the subminiature wedge bulbs.

I think, however, Stealth Amusements may sell the replacements you are looking for if they resemble these: http://stealthhome.stores.yahoo.net/t5buforsaty.html