That is a neat gun. I recently sold a Haenel Sportmodell 33...
H&N used to make 4.4 mm lead balls (don't know if they still do). JG airguns sold 4.4 mm balls by the pound, but it was just BB size shotgun pellets, so wasn't very round and didn't shoot accurately out of my Haenel rifled guns. Cheap though, he may still carry it.
Another cool military trainer is the Anschutz/Hakim in .22 (2nd gun down from top)