Dear flyingtorquewrench:
try
www.rent-a-jet.de which is the website of a German operator named FAI in Nürnberg who does a lot of contract work for the UN in Africa, currently with 2 LearJet 55, if I'm not mistaken.
Out of personal experience, I would
not recommend anybody to work there fully employed (don't ask!), but for a free-lancer the conditions are good and they're always looking for people. Last time I heard, they are paying 12,000€ / month for a LJ-driver in the left seat. Good luck!