Hi,
dcraw2hdrgen should be in pfscalibration package, which so far has not
been included in Ubuntu packages, so you need to compile it from the
sources.
I need to warn you that pfscalibration has not been maintained for a
long time and is not in the best shape. There is a long list of bugs
and TODO items, which I cannot handle myself because of lack of time.
Cheers,
Rafal