Through out the year there are bus from Lucerne to Pozega, the bus travels via Zagreb where passengers has to change bus. The bus departure from the bus terminal at Inseliquai, which is in the centre of Lucerne, just next to the train station. The bus travel time from Lucerne to Pozega is about 15 hours. If you are doing a roundtrip you should buy a return ticket as they are cheaper, you can see return timetable here.