You could ask in the Europe port forum
List your ports it will be easier to answer.
Lots of people on Oceania are well travelled & do private tours.
You might be able to sign up with some of them on the Roll Call of various cruise forums
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012