German nominalization -- tool ?

Hi,

I am looking for a morphological database/tool that can deliver the 
following nominalizations for German:

erfinden -> Erfinder
singen -> Saenger
handeln -> Haendler
etc.

Everything I've looked at so far had problems with irregularities (the 
last two cases)
Does anyone know a reliable tool?

Best regards,
Michaela Atterer