Børge,
If you can live with the slow operation, stay with the base ISO most of the time and can carry multiple spare batteries all the time, a FOVEON sensor cameras of Sigma may be one of a few solutions.
DP-1, -2 and -3 Merrill models have fixed lens, and SD1 Merrill is a Sigma mount DSLR. The sensor has full 15MP pixels in all R, G, B channels (layers) and could be used with yellow, orange, red or green filters for B&W films without losing the resolution which is a major problem with the beyer sensors.
The latest Quattro series would not be suitable for the purpose, because the green and red channels (layers) have 4x larger pixels and thus don't offer the full resolution.