. . .have used "cold cathode" flourescents (24volt). These are what people are nowadays using to light up the underside of their cars and the inside of their PCs. Only thing is, I haven`t seen them in white. Might be worth a little searching.
I don't know if it will help but I recall that a few years back someone wrote to one of the magazines regarding a failed lamp in an Agfa scanner and said that he had been quoted an horrific price to replace it.
He found that by taking the dead lamp to an electrical wholesaler (not Curry's or anywhere like that but the sort of place the 'sparks' go for their bits 'n bobs) the lamp turned out to be a standard part and bought one for a few pounds.
If you do find one like that you may have to re-calibrate the scanner due to the change of colour which aging causes in the lamp.